Changeset 0f9e4403 for doc/refrat/refrat.tex
- Timestamp:
- Apr 15, 2016, 12:03:11 PM (10 years ago)
- Branches:
- ADT, aaron-thesis, arm-eh, ast-experimental, cleanup-dtors, ctor, deferred_resn, demangler, enum, forall-pointer-decay, gc_noraii, jacob/cs343-translation, jenkins-sandbox, master, memory, new-ast, new-ast-unique-expr, new-env, no_list, persistent-indexer, pthread-emulation, qualifiedEnum, resolv-new, stuck-waitfor-destruct, with_gc
- Children:
- 29ad0ac
- Parents:
- c5833e8 (diff), 37f0da8 (diff)
Note: this is a merge changeset, the changes displayed below correspond to the merge itself.
Use the(diff)links above to see all the changes relative to each parent. - File:
-
- 1 edited
-
doc/refrat/refrat.tex (modified) (151 diffs)
Legend:
- Unmodified
- Added
- Removed
-
doc/refrat/refrat.tex
rc5833e8 r0f9e4403 1 %%%%%%%%%%%%%%%%%%%%%%%%%%%%%% -*- Mode: Latex -*- %%%%%%%%%%%%%%%%%%%%%%%%%%%% 2 %% 3 %% Cforall Version 1.0.0 Copyright (C) 2016 University of Waterloo 4 %% 5 %% The contents of this file are covered under the licence agreement in the 6 %% file "LICENCE" distributed with Cforall. 7 %% 8 %% refrat.tex -- 9 %% 10 %% Author : Peter A. Buhr 11 %% Created On : Wed Apr 6 14:52:25 2016 12 %% Last Modified By : Peter A. Buhr 13 %% Last Modified On : Sat Apr 9 10:19:12 2016 14 %% Update Count : 8 15 %%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%% 16 1 17 % requires tex packages: texlive-base texlive-latex-base tex-common texlive-humanities texlive-latex-extra texlive-fonts-recommended 2 18 … … 5 21 6 22 % Latex packages used in the document. 7 8 23 \usepackage{fullpage,times} 9 24 \usepackage{xspace} … … 11 26 \usepackage{listings} 12 27 \usepackage{comment} 13 \usepackage{latexsym} % \Box14 \usepackage{mathptmx} % better math font with "times"28 \usepackage{latexsym} % \Box 29 \usepackage{mathptmx} % better math font with "times" 15 30 \usepackage[pagewise]{lineno} 16 31 \renewcommand{\linenumberfont}{\scriptsize\sffamily} 17 32 \usepackage[dvips,plainpages=false,pdfpagelabels,pdfpagemode=UseNone,colorlinks=true,pagebackref=true,linkcolor=blue,citecolor=blue,urlcolor=blue,pagebackref=true,breaklinks=true]{hyperref} 18 33 \usepackage{breakurl} 19 \ urlstyle{sf}34 \renewcommand{\UrlFont}{\small\sf} 20 35 21 36 %%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%% 22 37 23 % Names used in the document. 24 25 \newcommand{\CFA}{Cforall\xspace} % set language text name 26 \newcommand{\CFAA}{C$\forall$\xspace} % set language symbolic name 27 \newcommand{\CC}{C\kern-.1em\hbox{+\kern-.25em+}\xspace} % CC symbolic name 28 \def\c11{ISO/IEC C} % C11 name (cannot have numbers in latex command name) 38 % Bespoke macros used in the document. 39 \input{common} 29 40 30 41 %%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%% 31 42 32 % Bespoke macros used in the document. 33 34 \makeatletter 35 % index macros 36 \newcommand{\italic}[1]{\emph{\hyperpage{#1}}} 37 \newcommand{\definition}[1]{\textbf{\hyperpage{#1}}} 38 \newcommand{\see}[1]{\emph{see} #1} 39 40 % Define some commands that produce formatted index entries suitable for cross-references. 41 % ``\spec'' produces entries for specifications of entities. ``\impl'' produces entries for their 42 % implementations, and ``\use'' for their uses. 43 44 % \newcommand{\bold}[1]{{\bf #1}} 45 % \def\spec{\@bsphack\begingroup 46 % \def\protect##1{\string##1\space}\@sanitize 47 % \@wrxref{|bold}} 48 \def\impl{\@bsphack\begingroup 49 \def\protect##1{\string##1\space}\@sanitize 50 \@wrxref{|definition}} 51 \newcommand{\indexcode}[1]{{\lstinline$#1$}} 52 \def\use{\@bsphack\begingroup 53 \def\protect##1{\string##1\space}\@sanitize 54 \@wrxref{|hyperpage}} 55 \def\@wrxref#1#2{\let\thepage\relax 56 \xdef\@gtempa{\write\@indexfile{\string 57 \indexentry{#2@{\lstinline$#2$}#1}{\thepage}}}\endgroup\@gtempa 58 \if@nobreak \ifvmode\nobreak\fi\fi\@esphack} 59 %\newcommand{\use}[1]{\index{#1@{\lstinline$#1$}}} 60 %\newcommand{\impl}[1]{\index{\protect#1@{\lstinline$\protect#1$}|definition}} 61 62 % text inline and lowercase index: \Index{Inline and index text} 63 % text inline and as-in index: \Index{Inline and Index text} 64 % text inline but index with different as-is text: \Index[index text]{inline text} 65 \newcommand{\Index}{\@ifstar\@sIndex\@Index} 66 \newcommand{\@Index}[2][\@empty]{\lowercase{\def\temp{#2}}#2\ifx#1\@empty\index{\temp}\else\index{#1@{\protect#2}}\fi} 67 \newcommand{\@sIndex}[2][\@empty]{#2\ifx#1\@empty\index{#2}\else\index{#1@{\protect#2}}\fi} 68 \makeatother 69 70 % blocks and titles 71 \newcommand{\define}[1]{\emph{#1\/}\index{#1}} 72 \newenvironment{rationale}{% 73 \begin{quotation}\noindent$\Box$\enspace 74 }{% 75 \hfill\enspace$\Box$\end{quotation} 76 }% 77 \newcommand{\rewrite}{\(\Rightarrow\)} 78 \newcommand{\rewriterules}{\paragraph{Rewrite Rules}~\par\noindent} 79 \newcommand{\examples}{\paragraph{Examples}~\par\noindent} 80 \newcommand{\semantics}{\paragraph{Semantics}~\par\noindent} 81 \newcommand{\constraints}{\paragraph{Constraints}~\par\noindent} 82 \newcommand{\predefined}{\paragraph{Predefined Identifiers}~\par\noindent} 83 84 % BNF macros 85 \def\syntax{\paragraph{Syntax}\trivlist\parindent=.5in\item[\hskip.5in]} 86 \let\endsyntax=\endtrivlist 87 \newcommand{\lhs}[1]{\par{\emph{#1:}}\index{#1@{\emph{#1}}|italic}} 88 \newcommand{\rhs}{\hfil\break\hbox{\hskip1in}} 89 \newcommand{\oldlhs}[1]{\emph{#1: \ldots}\index{#1@{\emph{#1}}|italic}} 90 \newcommand{\nonterm}[1]{\emph{#1\/}\index{#1@{\emph{#1}}|italic}} 91 \newcommand{\opt}{$_{opt}$\ } 92 93 % adjust varioref package with default "section" and "page" titles, and optional title with faraway page numbers 94 % \VRef{label} => Section 2.7, \VPageref{label} => page 17 95 % \VRef[Figure]{label} => Figure 3.4, \VPageref{label} => page 17 96 \renewcommand{\reftextfaceafter}{\unskip} 97 \renewcommand{\reftextfacebefore}{\unskip} 98 \renewcommand{\reftextafter}{\unskip} 99 \renewcommand{\reftextbefore}{\unskip} 100 \renewcommand{\reftextfaraway}[1]{\unskip, p.~\pageref{#1}} 101 \renewcommand{\reftextpagerange}[2]{\unskip, pp.~\pageref{#1}--\pageref{#2}} 102 \newcommand{\VRef}[2][Section]{\ifx#1\@empty\else{#1}\nobreakspace\fi\vref{#2}} 103 \newcommand{\VPageref}[2][page]{\ifx#1\@empty\else{#1}\nobreakspace\fi\pageref{#2}} 104 105 % adjust listings macros 106 \lstdefinelanguage{CFA}[ANSI]{C}% 107 {morekeywords={asm,_Alignas,_Alignof,_At,_Atomic,_Bool,catch,catchResume,choose,_Complex,context,disable,dtype,enable, 108 fallthru,finally,forall,ftype,_Generic,_Imaginary,inline,lvalue,_Noreturn,restrict,_Static_assert, 109 _Thread_local,throw,throwResume,try,type,}, 110 }% 111 112 \lstset{ 113 language=CFA, 114 columns=flexible, 115 basicstyle=\sf\small, 116 tabsize=4, 117 xleftmargin=\parindent, 118 escapechar=@, 119 keepspaces=true, 120 %showtabs=true, 121 %tab=\rightarrowfill, 122 }% 123 124 \makeatletter 125 % replace/adjust listings characters that look bad in sanserif 126 \lst@CCPutMacro 127 \lst@ProcessOther{"2D}{\lst@ttfamily{-{}}{{\ttfamily\upshape -}}} % replace minus 128 \lst@ProcessOther{"3C}{\lst@ttfamily{<}{\texttt{<}}} % replace less than 129 \lst@ProcessOther{"3E}{\lst@ttfamily{<}{\texttt{>}}} % replace greater than 130 \lst@ProcessOther{"5E}{\raisebox{0.4ex}{$\scriptstyle\land\,$}} % replace circumflex 131 \lst@ProcessLetter{"5F}{\lst@ttfamily{\char95}{{\makebox[1.2ex][c]{\rule{1ex}{0.1ex}}}}} % replace underscore 132 \lst@ProcessOther{"7E}{\raisebox{0.3ex}{$\scriptstyle\sim\,$}} % replace tilde 133 %\lst@ProcessOther{"7E}{\raisebox{-.4ex}[1ex][0pt]{\textasciitilde}} % lower tilde 134 \@empty\z@\@empty 135 \makeatother 136 137 \setcounter{secnumdepth}{3} % number subsubsections 138 \setcounter{tocdepth}{3} % subsubsections in table of contents 43 \setcounter{secnumdepth}{3} % number subsubsections 44 \setcounter{tocdepth}{3} % subsubsections in table of contents 139 45 \makeindex 140 46 … … 143 49 \begin{document} 144 50 \pagestyle{headings} 145 \linenumbers % comment out to turn off line numbering 146 147 \title{\CFA (\CFAA) Reference Manual and Rationale} 148 \author{Glen Ditchfield \and Peter A. Buhr} 149 \date{DRAFT\\\today} 51 \linenumbers % comment out to turn off line numbering 52 53 \title{\Huge 54 \vspace*{1in} 55 \CFA (\CFL) Reference Manual and Rationale 56 }% title 57 \author{\huge 58 Glen Ditchfield and Peter A. Buhr 59 }% author 60 \date{ 61 DRAFT\\\today 62 }% date 150 63 151 64 \pagenumbering{roman} … … 159 72 \copyright\,2015 Glen Ditchfield \\ \\ 160 73 \noindent 161 This work is licensed under the Creative Commons Attribution 4.0 International License. To view a162 copy of this license, visit {\small\url{http://creativecommons.org/licenses/by/4.0}}.74 This work is licensed under the Creative Commons Attribution 4.0 International License. 75 To view a copy of this license, visit {\small\url{http://creativecommons.org/licenses/by/4.0}}. 163 76 \vspace*{1in} 164 77 … … 173 86 \chapter*{Introduction}\addcontentsline{toc}{chapter}{Introduction} 174 87 175 This document is a reference manual and rationale for \CFA, a polymorphic extension of the C 176 programming language. It makes frequent reference to the {\c11} standard \cite{ANS:C11}, and 177 occasionally compares \CFA to {\CC} \cite{c++}. 178 179 The manual deliberately imitates the ordering of the {\c11} standard (although the section numbering 180 differs). Unfortunately, this means the manual contains more ``forward references'' than usual, 181 making it harder to follow if the reader does not have a copy of the {\c11} standard. For a simple 182 introduction to \CFA, see the companion document ``An Overview of \CFA'' 88 This document is a reference manual and rationale for \CFA, a polymorphic extension of the C programming language. 89 It makes frequent reference to the {\c11} standard \cite{C11}, and occasionally compares \CFA to {\CC} \cite{C++}. 90 91 The manual deliberately imitates the ordering of the {\c11} standard (although the section numbering differs). 92 Unfortunately, this means the manual contains more ``forward references'' than usual, making it harder to follow if the reader does not have a copy of the {\c11} standard. 93 For a simple introduction to \CFA, see the companion document ``An Overview of \CFA'' 183 94 \cite{Ditchfield96:Overview}. 184 95 185 96 \begin{rationale} 186 Commentary (like this) is quoted with quads. Commentary usually deals with subtle points, the187 rationale behind a rule, and design decisions.97 Commentary (like this) is quoted with quads. 98 Commentary usually deals with subtle points, the rationale behind a rule, and design decisions. 188 99 \end{rationale} 189 100 … … 194 105 \chapter{Terms, definitions, and symbols} 195 106 196 Terms from the {\c11} standard used in this document have the same meaning as in the {\c11} 197 standard. 107 Terms from the {\c11} standard used in this document have the same meaning as in the {\c11} standard. 198 108 199 109 % No ``Conformance'' or ``Environment'' chapters yet. … … 205 115 206 116 \section{Notation} 207 The syntax notation used in this document is the same as in the {\c11} standard, with one exception: 208 ellipsis in the definition of a nonterminal, as in ``\emph{declaration:} \ldots'', indicates that 209 these rules extend a previous definition, which occurs in this document or in the {\c11} standard. 117 The syntax notation used in this document is the same as in the {\c11} standard, with one exception: ellipsis in the definition of a nonterminal, as in ``\emph{declaration:} \ldots'', indicates that these rules extend a previous definition, which occurs in this document or in the {\c11} standard. 210 118 211 119 … … 215 123 \subsection{Scopes of identifiers}\index{scopes} 216 124 217 \CFA's scope rules differ from C's in one major respect: a declaration of an identifier may 218 overload\index{overloading} outer declarations of lexically identical identifiers in the same 219 \Index{name space}, instead of hiding them. The outer declaration is hidden if the two declarations 220 have \Index{compatible type}, or if one declares an array type and the other declares a pointer type 221 and the element type and pointed-at type are compatible, or if one has function type and the other 222 is a pointer to a compatible function type, or if one declaration is a \lstinline$type$\use{type} or 125 \CFA's scope rules differ from C's in one major respect: a declaration of an identifier may overload\index{overloading} outer declarations of lexically identical identifiers in the same 126 \Index{name space}, instead of hiding them. 127 The outer declaration is hidden if the two declarations have \Index{compatible type}, or if one declares an array type and the other declares a pointer type and the element type and pointed-at type are compatible, or if one has function type and the other is a pointer to a compatible function type, or if one declaration is a \lstinline$type$\use{type} or 223 128 \lstinline$typedef$\use{typedef} declaration and the other is not. The outer declaration becomes 224 129 \Index{visible} when the scope of the inner declaration terminates. 225 130 \begin{rationale} 226 Hence, a \CFA program can declare an \lstinline$int v$ and a \lstinline$float v$ in the same 227 scope;a {\CC} program can not.131 Hence, a \CFA program can declare an \lstinline$int v$ and a \lstinline$float v$ in the same scope; 132 a {\CC} program can not. 228 133 \end{rationale} 229 134 … … 232 137 \index{linkage} 233 138 234 \CFA's linkage rules differ from C's in only one respect: instances of a particular identifier with 235 external or internal linkage do not necessarily denote the same object or function. Instead, in the 236 set of translation units and libraries that constitutes an entire program, any two instances of a 237 particular identifier with \Index{external linkage} denote the same object or function if they have 238 \Index{compatible type}s, or if one declares an array type and the other declares a pointer type and 239 the element type and pointed-at type are compatible, or if one has function type and the other is a 240 pointer to a compatible function type. Within one translation unit, each instance of an identifier 241 with \Index{internal linkage} denotes the same object or function in the same circumstances. 139 \CFA's linkage rules differ from C's in only one respect: instances of a particular identifier with external or internal linkage do not necessarily denote the same object or function. 140 Instead, in the set of translation units and libraries that constitutes an entire program, any two instances of a particular identifier with \Index{external linkage} denote the same object or function if they have 141 \Index{compatible type}s, or if one declares an array type and the other declares a pointer type and the element type and pointed-at type are compatible, or if one has function type and the other is a pointer to a compatible function type. 142 Within one translation unit, each instance of an identifier with \Index{internal linkage} denotes the same object or function in the same circumstances. 242 143 Identifiers with \Index{no linkage} always denote unique entities. 243 144 \begin{rationale} 244 A \CFA program can declare an \lstinline$extern int v$ and an \lstinline$extern float v$; a C245 program cannot.145 A \CFA program can declare an \lstinline$extern int v$ and an \lstinline$extern float v$; 146 a C program cannot. 246 147 \end{rationale} 247 148 … … 253 154 \subsubsection{Semantics} 254 155 255 \CFA provides a capability for generic types; using this capability a single "generic type 256 generator" can be written that can represent multiple concrete type instantiations by substitution 257 of the "type parameters" of the generic type for concrete types. Syntactically a generic type 258 generator is represented by putting a forall specifier on a struct or union declaration, as defined 259 in \VRef{forall}. An instantiation of the generic type is written by specifying the type parameters 260 in parentheses after the name of the generic type generator: 261 \begin{lstlisting} 262 forall( type T | sumable( T ) ) struct pair { 156 \CFA provides a capability for generic types; 157 using this capability a single "generic type generator" can be written that can represent multiple concrete type instantiations by substitution of the "type parameters" of the generic type for concrete types. 158 Syntactically a generic type generator is represented by putting a forall specifier on a struct or union declaration, as defined in \VRef{forall}. 159 An instantiation of the generic type is written by specifying the type parameters in parentheses after the name of the generic type generator: 160 \begin{lstlisting} 161 forall( otype T | sumable( T ) ) struct pair { 263 162 T x; 264 163 T y; … … 267 166 \end{lstlisting} 268 167 269 The type parameters in an instantiation of a generic type must satisfy any constraints in the forall 270 specifier on the type generator declaration, e.g., \lstinline$sumable$. The instantiation then has 271 the semantics that would result if the type parameters were substituted into the type generator 272 declaration by macro substitution. 273 274 Polymorphic functions may have generic types as parameters, and those generic types may use type 275 parameters of the polymorphic function as type parameters of the generic type: 276 \begin{lstlisting} 277 forall( type T ) void swap( pair(T) *p ) { 168 The type parameters in an instantiation of a generic type must satisfy any constraints in the forall specifier on the type generator declaration, e.g., \lstinline$sumable$. 169 The instantiation then has the semantics that would result if the type parameters were substituted into the type generator declaration by macro substitution. 170 171 Polymorphic functions may have generic types as parameters, and those generic types may use type parameters of the polymorphic function as type parameters of the generic type: 172 \begin{lstlisting} 173 forall( otype T ) void swap( pair(T) *p ) { 278 174 T z = p->x; 279 175 p->x = p->y; … … 285 181 \subsubsection{Constraints} 286 182 287 To avoid unduly constraining implementors, the generic type generator definition must be visible at 288 any point where it is instantiated. Forward declarations of generic type generators are not 289 forbidden, but the definition must be visible to instantiate the generic type. Equivalently, 290 instantiations of generic types are not allowed to be incomplete types. 183 To avoid unduly constraining implementors, the generic type generator definition must be visible at any point where it is instantiated. 184 Forward declarations of generic type generators are not forbidden, but the definition must be visible to instantiate the generic type. Equivalently, instantiations of generic types are not allowed to be incomplete types. 291 185 292 186 \examples 293 187 \begin{lstlisting} 294 forall( type T ) struct A;295 296 forall( type T ) struct B {297 A(T) *a; // legal, but cannot instantiate B(T)188 forall( otype T ) struct A; 189 190 forall( otype T ) struct B { 191 A(T) *a; // legal, but cannot instantiate B(T) 298 192 }; 299 193 300 B(T) x; // illegal, *x.a is of an incomplete generic type301 302 forall( type T ) struct A {194 B(T) x; // illegal, *x.a is of an incomplete generic type 195 196 forall( otype T ) struct A { 303 197 B( T ) *b; 304 198 }; 305 199 306 B( T ) y; // legal, *x.a is now of a complete generic type 307 200 B( T ) y; // legal, *x.a is now of a complete generic type 308 201 309 202 // box.h: 310 forall( type T ) struct box;311 forall( type T ) box( T ) *make_box( T );312 forall( type T ) void use_box( box( T ) *b );203 forall( otype T ) struct box; 204 forall( otype T ) box( T ) *make_box( T ); 205 forall( otype T ) void use_box( box( T ) *b ); 313 206 314 207 // main.c: 315 box( int ) *b = make_box( 42 ); // illegal, def 'n of box not visible316 use_box( b ); // illegal208 box( int ) *b = make_box( 42 ); // illegal, definition of box not visible 209 use_box( b ); // illegal 317 210 \end{lstlisting} 318 211 … … 320 213 \section{Conversions} 321 214 \CFA defines situations where values of one type are automatically converted to another type. 322 These conversions are called \define{implicit conversion}s. The programmer can request 215 These conversions are called \define{implicit conversion}s. 216 The programmer can request 323 217 \define{explicit conversion}s using cast expressions. 324 218 … … 330 224 \subsubsection{Safe arithmetic conversions} 331 225 332 In C, a pattern of conversions known as the \define{usual arithmetic conversion}s is used with most 333 binary arithmetic operators to convert the operands to a common type and determine the type of the 334 operator's result. In \CFA, these conversions play a role in overload resolution, and 335 collectively are called the \define{safe arithmetic conversion}s. 336 337 Let \(int_r\) and \(unsigned_r\) be the signed and unsigned integer types with integer conversion 338 rank\index{integer conversion rank}\index{rank|see{integer conversion rank}} $r$. Let 339 \(unsigned_{mr}\) be the unsigned integer type with maximal rank. 226 In C, a pattern of conversions known as the \define{usual arithmetic conversion}s is used with most binary arithmetic operators to convert the operands to a common type and determine the type of the operator's result. 227 In \CFA, these conversions play a role in overload resolution, and collectively are called the \define{safe arithmetic conversion}s. 228 229 Let \(int_r\) and \(unsigned_r\) be the signed and unsigned integer types with integer conversion rank\index{integer conversion rank}\index{rank|see{integer conversion rank}} $r$. 230 Let \(unsigned_{mr}\) be the unsigned integer type with maximal rank. 340 231 341 232 The following conversions are \emph{direct} safe arithmetic conversions. … … 343 234 \item 344 235 The \Index{integer promotion}s. 345 346 \item 347 For every rank $r$ greater than or equal to the rank of \lstinline$int$, conversion from \(int_r\) 348 to \(unsigned_r\). 349 350 \item 351 For every rank $r$ greater than or equal to the rank of \lstinline$int$, where \(int_{r+1}\) exists 352 and can represent all values of \(unsigned_r\), conversion from \(unsigned_r\) to \(int_{r+1}\). 353 236 \item 237 For every rank $r$ greater than or equal to the rank of \lstinline$int$, conversion from \(int_r\) to \(unsigned_r\). 238 \item 239 For every rank $r$ greater than or equal to the rank of \lstinline$int$, where \(int_{r+1}\) exists and can represent all values of \(unsigned_r\), conversion from \(unsigned_r\) to \(int_{r+1}\). 354 240 \item 355 241 Conversion from \(unsigned_{mr}\) to \lstinline$float$. 356 357 242 \item 358 243 Conversion from an enumerated type to its compatible integer type. 359 360 \item 361 Conversion from \lstinline$float$ to \lstinline$double$, and from \lstinline$double$ to 362 \lstinline$long double$. 363 364 \item 365 Conversion from \lstinline$float _Complex$ to \lstinline$double _Complex$, 366 and from \lstinline$double _Complex$ to \lstinline$long double _Complex$. 367 244 \item 245 Conversion from \lstinline$float$ to \lstinline$double$, and from \lstinline$double$ to \lstinline$long double$. 246 \item 247 Conversion from \lstinline$float _Complex$ to \lstinline$double _Complex$, and from \lstinline$double _Complex$ to \lstinline$long double _Complex$. 368 248 \begin{sloppypar} 369 249 \item 370 Conversion from \lstinline$float _Imaginary$ to \lstinline$double _Imaginary$, and from 371 \lstinline$double _Imaginary$ to \lstinline$long double$ \lstinline$_Imaginary$, if the 372 implementation supports imaginary types. 250 Conversion from \lstinline$float _Imaginary$ to \lstinline$double _Imaginary$, and from \lstinline$double _Imaginary$ to \lstinline$long double$ \lstinline$_Imaginary$, if the implementation supports imaginary types. 373 251 \end{sloppypar} 374 252 \end{itemize} 375 253 376 If type \lstinline$T$ can be converted to type \lstinline$U$ by a safe direct arithmetic conversion 377 and type \lstinline$U$ can be converted to type \lstinline$V$ by a safe arithmetic conversion, then 378 the conversion from \lstinline$T$ to type \lstinline$V$ is an \emph{indirect} safe arithmetic 379 conversion. 380 381 \begin{rationale} 382 Note that {\c11} does not include conversion from \Index{real type}s to \Index{complex type}s in the 383 usual arithmetic conversions, and \CFA does not include them as safe conversions. 254 If type \lstinline$T$ can be converted to type \lstinline$U$ by a safe direct arithmetic conversion and type \lstinline$U$ can be converted to type \lstinline$V$ by a safe arithmetic conversion, then the conversion from \lstinline$T$ to type \lstinline$V$ is an \emph{indirect} safe arithmetic conversion. 255 256 \begin{rationale} 257 Note that {\c11} does not include conversion from \Index{real type}s to \Index{complex type}s in the usual arithmetic conversions, and \CFA does not include them as safe conversions. 384 258 \end{rationale} 385 259 … … 393 267 394 268 If an expression's type is a pointer to a structure or union type that has a member that is an 395 \Index{anonymous structure} or an \Index{anonymous union}, it can be implicitly 396 converted\index{implicit conversion} to a pointer to the anonymous structure's or anonymous union's 397 type. The result of the conversion is a pointer to the member. 269 \Index{anonymous structure} or an \Index{anonymous union}, it can be implicitly converted\index{implicit conversion} to a pointer to the anonymous structure's or anonymous union's type. 270 The result of the conversion is a pointer to the member. 398 271 399 272 \examples … … 402 275 int x, y; 403 276 }; 404 void move_by( struct point * p1, struct point * p2) {@\impl{move_by}@277 void move_by( struct point * p1, struct point * p2 ) {@\impl{move_by}@ 405 278 p1->x += p2.x; 406 279 p1->y += p2.y; 407 280 } 408 409 281 struct color_point { 410 282 enum { RED, BLUE, GREEN } color; 411 283 struct point; 412 284 } cp1, cp2; 413 move_to( &cp1, &cp2);285 move_to( &cp1, &cp2 ); 414 286 \end{lstlisting} 415 287 Thanks to implicit conversion, the two arguments that \lstinline$move_by()$ receives are pointers to … … 418 290 419 291 \subsubsection{Specialization} 420 A function or value whose type is polymorphic may be implicitly converted to one whose type is 421 \Index{less polymorphic} by binding values to one or more of its \Index{inferred parameter}. Any 422 value that is legal for the inferred parameter may be used, including other inferred parameters. 423 424 If, after the inferred parameter binding, an \Index{assertion parameter} has no inferred parameters 425 in its type, then an object or function must be visible at the point of the specialization that has 426 the same identifier as the assertion parameter and has a type that is compatible\index{compatible 427 type} with or can be specialized to the type of the assertion parameter. The assertion parameter 428 is bound to that object or function. 429 430 The type of the specialization is the type of the original with the bound inferred parameters and 431 the bound assertion parameters replaced by their bound values. 292 A function or value whose type is polymorphic may be implicitly converted to one whose type is \Index{less polymorphic} by binding values to one or more of its \Index{inferred parameter}. 293 Any value that is legal for the inferred parameter may be used, including other inferred parameters. 294 295 If, after the inferred parameter binding, an \Index{assertion parameter} has no inferred parameters in its type, then an object or function must be visible at the point of the specialization that has the same identifier as the assertion parameter and has a type that is compatible\index{compatible type} with or can be specialized to the type of the assertion parameter. 296 The assertion parameter is bound to that object or function. 297 298 The type of the specialization is the type of the original with the bound inferred parameters and the bound assertion parameters replaced by their bound values. 432 299 433 300 \examples 434 301 The type 435 302 \begin{lstlisting} 436 forall( type T,type U ) void (*)( T, U );303 forall( otype T, otype U ) void (*)( T, U ); 437 304 \end{lstlisting} 438 305 can be specialized to (among other things) 439 306 \begin{lstlisting} 440 forall( type T ) void (*)( T, T ); // U bound to T441 forall( type T ) void (*)( T, real ); // U bound to real442 forall( type U ) void (*)( real, U ); // T bound to real307 forall( otype T ) void (*)( T, T ); // U bound to T 308 forall( otype T ) void (*)( T, real ); // U bound to real 309 forall( otype U ) void (*)( real, U ); // T bound to real 443 310 void f( real, real ); // both bound to real 444 311 \end{lstlisting} … … 446 313 The type 447 314 \begin{lstlisting} 448 forall( type T | T ?+?( T, T )) T (*)( T );315 forall( otype T | T ?+?( T, T ) ) T (*)( T ); 449 316 \end{lstlisting} 450 317 can be specialized to (among other things) 451 318 \begin{lstlisting} 452 int (*)( int ); // T bound to int, and T ?+?(T, T ) bound to int ?+?( int, int )319 int (*)( int ); // T bound to int, and T ?+?(T, T ) bound to int ?+?( int, int ) 453 320 \end{lstlisting} 454 321 … … 465 332 from a pointer to any non-\lstinline$void$ type to a pointer to \lstinline$void$; 466 333 \item 467 from a pointer to any type to a pointer to a more qualified version of the type\index{qualified 468 type}; 469 \item 470 from a pointer to a structure or union type to a pointer to the type of a member of the structure or 471 union that is an \Index{anonymous structure} or an \Index{anonymous union}; 472 \item 473 within the scope of an initialized \Index{type declaration}, conversions between a type and its 474 implementation or between a pointer to a type and a pointer to its implementation. 334 from a pointer to any type to a pointer to a more qualified version of the type\index{qualified type}; 335 \item 336 from a pointer to a structure or union type to a pointer to the type of a member of the structure or union that is an \Index{anonymous structure} or an \Index{anonymous union}; 337 \item 338 within the scope of an initialized \Index{type declaration}, conversions between a type and its implementation or between a pointer to a type and a pointer to its implementation. 475 339 \end{itemize} 476 340 477 341 Conversions that are not safe conversions are \define{unsafe conversion}s. 478 342 \begin{rationale} 479 As in C, there is an implicit conversion from \lstinline$void *$ to any pointer type. This is 480 clearly dangerous, and {\CC} does not have this implicit conversion. 481 \CFA\index{deficiencies!void * conversion} keeps it, in the interest of remaining as pure a 482 superset of C as possible, but discourages it by making it unsafe. 343 As in C, there is an implicit conversion from \lstinline$void *$ to any pointer type. 344 This is clearly dangerous, and {\CC} does not have this implicit conversion. 345 \CFA\index{deficiencies!void * conversion} keeps it, in the interest of remaining as pure a superset of C as possible, but discourages it by making it unsafe. 483 346 \end{rationale} 484 347 … … 486 349 \subsection{Conversion cost} 487 350 488 The \define{conversion cost} of a safe\index{safe conversion} 489 conversion\footnote{Unsafe\index{unsafe conversion} conversions do not have defined conversion 490 costs.} is a measure of how desirable or undesirable it is. It is defined as follows. 351 The \define{conversion cost} of a safe\index{safe conversion} conversion\footnote{Unsafe\index{unsafe conversion} conversions do not have defined conversion costs.} is a measure of how desirable or undesirable it is. 352 It is defined as follows. 491 353 \begin{itemize} 492 354 \item … … 497 359 498 360 \item 499 The cost of an indirect safe arithmetic conversion is the smallest number of direct conversions 500 needed to make up the conversion. 361 The cost of an indirect safe arithmetic conversion is the smallest number of direct conversions needed to make up the conversion. 501 362 \end{itemize} 502 363 … … 506 367 \begin{itemize} 507 368 \item 508 The cost of an implicit conversion from \lstinline$int$ to \lstinline$long$ is 1. The cost of an 509 implicit conversion from \lstinline$long$ to \lstinline$double$ is 3, because it is defined in terms 510 of conversions from \lstinline$long$ to \lstinline$unsigned long$, then to \lstinline$float$, and 511 then to \lstinline$double$. 512 513 \item 514 If \lstinline$int$ can represent all the values of \lstinline$unsigned short$, then the cost of an 515 implicit conversion from \lstinline$unsigned short$ to \lstinline$unsigned$ is 2: 516 \lstinline$unsigned short$ to \lstinline$int$ to \lstinline$unsigned$. Otherwise, 517 \lstinline$unsigned short$ is converted directly to \lstinline$unsigned$, and the cost is 1. 518 519 \item 520 If \lstinline$long$ can represent all the values of \lstinline$unsigned$, then the conversion cost 521 of \lstinline$unsigned$ to \lstinline$long$ is 1. Otherwise, the conversion is an unsafe 522 conversion, and its conversion cost is undefined. 369 The cost of an implicit conversion from \lstinline$int$ to \lstinline$long$ is 1. 370 The cost of an implicit conversion from \lstinline$long$ to \lstinline$double$ is 3, because it is defined in terms of conversions from \lstinline$long$ to \lstinline$unsigned long$, then to \lstinline$float$, and then to \lstinline$double$. 371 372 \item 373 If \lstinline$int$ can represent all the values of \lstinline$unsigned short$, then the cost of an implicit conversion from \lstinline$unsigned short$ to \lstinline$unsigned$ is 2: 374 \lstinline$unsigned short$ to \lstinline$int$ to \lstinline$unsigned$. 375 Otherwise, \lstinline$unsigned short$ is converted directly to \lstinline$unsigned$, and the cost is 1. 376 377 \item 378 If \lstinline$long$ can represent all the values of \lstinline$unsigned$, then the conversion cost of \lstinline$unsigned$ to \lstinline$long$ is 1. 379 Otherwise, the conversion is an unsafe conversion, and its conversion cost is undefined. 523 380 \end{itemize} 524 381 … … 529 386 \rhs \lstinline$forall$ 530 387 \rhs \lstinline$lvalue$ 531 \rhs \lstinline$ context$388 \rhs \lstinline$trait$ 532 389 \rhs \lstinline$dtype$ 533 390 \rhs \lstinline$ftype$ … … 538 395 \subsection{Identifiers} 539 396 540 \CFA allows operator \Index{overloading} by associating operators with special function 541 identifiers. Furthermore, the constants ``\lstinline$0$'' and ``\lstinline$1$'' have special status 542 for many of C's data types (and for many programmer-defined data types as well), so \CFA treats them 543 as overloadable identifiers. Programmers can use these identifiers to declare functions and objects 544 that implement operators and constants for their own types. 397 \CFA allows operator \Index{overloading} by associating operators with special function identifiers. 398 Furthermore, the constants ``\lstinline$0$'' and ``\lstinline$1$'' have special status for many of C's data types (and for many programmer-defined data types as well), so \CFA treats them as overloadable identifiers. 399 Programmers can use these identifiers to declare functions and objects that implement operators and constants for their own types. 545 400 546 401 … … 554 409 \end{syntax} 555 410 556 \index{constant identifiers}\index{identifiers!for constants} The tokens ``\lstinline$0$''\impl{0} 557 and ``\lstinline$1$''\impl{1} are identifiers. No other tokens defined by the rules for integer 558 constants are considered to be identifiers. 559 \begin{rationale} 560 Why ``\lstinline$0$'' and ``\lstinline$1$''? Those integers have special status in C. All scalar 561 types can be incremented and decremented, which is defined in terms of adding or subtracting 1. The 562 operations ``\lstinline$&&$'', ``\lstinline$||$'', and ``\lstinline$!$'' can be applied to any 563 scalar arguments, and are defined in terms of comparison against 0. A \nonterm{constant-expression} 564 that evaluates to 0 is effectively compatible with every pointer type. 565 566 In C, the integer constants 0 and 1 suffice because the integer promotion rules can convert them to 567 any arithmetic type, and the rules for pointer expressions treat constant expressions evaluating to 568 0 as a special case. However, user-defined arithmetic types often need the equivalent of a 1 or 0 569 for their functions or operators, polymorphic functions often need 0 and 1 constants of a type 570 matching their polymorphic parameters, and user-defined pointer-like types may need a null value. 571 Defining special constants for a user-defined type is more efficient than defining a conversion to 572 the type from \lstinline$_Bool$. 573 574 Why \emph{just} ``\lstinline$0$'' and ``\lstinline$1$''? Why not other integers? No other integers 575 have special status in C. A facility that let programmers declare specific 576 constants---``\lstinline$const Rational 12$'', for instance---would not be much of an improvement. 577 Some facility for defining the creation of values of programmer-defined types from arbitrary integer 578 tokens would be needed. The complexity of such a feature doesn't seem worth the gain. 411 \index{constant identifiers}\index{identifiers!for constants} The tokens ``\lstinline$0$''\impl{0} and ``\lstinline$1$''\impl{1} are identifiers. 412 No other tokens defined by the rules for integer constants are considered to be identifiers. 413 \begin{rationale} 414 Why ``\lstinline$0$'' and ``\lstinline$1$''? Those integers have special status in C. 415 All scalar types can be incremented and decremented, which is defined in terms of adding or subtracting 1. 416 The operations ``\lstinline$&&$'', ``\lstinline$||$'', and ``\lstinline$!$'' can be applied to any scalar arguments, and are defined in terms of comparison against 0. 417 A \nonterm{constant-expression} that evaluates to 0 is effectively compatible with every pointer type. 418 419 In C, the integer constants 0 and 1 suffice because the integer promotion rules can convert them to any arithmetic type, and the rules for pointer expressions treat constant expressions evaluating to 0 as a special case. 420 However, user-defined arithmetic types often need the equivalent of a 1 or 0 for their functions or operators, polymorphic functions often need 0 and 1 constants of a type matching their polymorphic parameters, and user-defined pointer-like types may need a null value. 421 Defining special constants for a user-defined type is more efficient than defining a conversion to the type from \lstinline$_Bool$. 422 423 Why \emph{just} ``\lstinline$0$'' and ``\lstinline$1$''? Why not other integers? No other integers have special status in C. 424 A facility that let programmers declare specific constants---``\lstinline$const Rational 12$'', for instance---would not be much of an improvement. 425 Some facility for defining the creation of values of programmer-defined types from arbitrary integer tokens would be needed. 426 The complexity of such a feature doesn't seem worth the gain. 579 427 \end{rationale} 580 428 … … 582 430 \subsubsection{Operator identifiers} 583 431 584 \index{operator identifiers}\index{identifiers!for operators} Table \ref{opids} lists the 585 programmer-definable operator identifiers and the operations they are associated with. Functions 586 that are declared with (or pointed at by function pointers that are declared with) these identifiers 587 can be called by expressions that use the operator tokens and syntax, or the operator identifiers 588 and ``function call'' syntax. The relationships between operators and function calls are discussed 589 in descriptions of the operators. 432 \index{operator identifiers}\index{identifiers!for operators} Table \ref{opids} lists the programmer-definable operator identifiers and the operations they are associated with. 433 Functions that are declared with (or pointed at by function pointers that are declared with) these identifiers can be called by expressions that use the operator tokens and syntax, or the operator identifiers and ``function call'' syntax. 434 The relationships between operators and function calls are discussed in descriptions of the operators. 590 435 591 436 \begin{table}[hbt] … … 644 489 645 490 \begin{rationale} 646 Operator identifiers are made up of the characters of the operator token, with question marks added 647 to mark the positions of the arguments of operators. The question marks serve as mnemonic devices; 648 programmers can not create new operators by arbitrarily mixing question marks and other 649 non-alphabetic characters. Note that prefix and postfix versions of the increment and decrement 650 operators are distinguished by the position of the question mark. 651 \end{rationale} 652 653 \begin{rationale} 654 The use of ``\lstinline$?$'' in identifiers means that some C programs are not \CFA programs. For 655 instance, the sequence of characters ``\lstinline$(i < 0)?--i:i$'' is legal in a C program, but a 656 \CFA compiler detects a syntax error because it treats ``\lstinline$?--$'' as an identifier, not 657 as the two tokens ``\lstinline$?$'' and ``\lstinline$--$''. 491 Operator identifiers are made up of the characters of the operator token, with question marks added to mark the positions of the arguments of operators. 492 The question marks serve as mnemonic devices; 493 programmers can not create new operators by arbitrarily mixing question marks and other non-alphabetic characters. 494 Note that prefix and postfix versions of the increment and decrement operators are distinguished by the position of the question mark. 495 \end{rationale} 496 497 \begin{rationale} 498 The use of ``\lstinline$?$'' in identifiers means that some C programs are not \CFA programs. For instance, the sequence of characters ``\lstinline$(i < 0)?--i:i$'' is legal in a C program, but a 499 \CFA compiler detects a syntax error because it treats ``\lstinline$?--$'' as an identifier, not as the two tokens ``\lstinline$?$'' and ``\lstinline$--$''. 658 500 \end{rationale} 659 501 … … 663 505 \item 664 506 The logical operators ``\lstinline$&&$'' and ``\lstinline$||$'', and the conditional operator 665 ``\lstinline$?:$''. These operators do not always evaluate their operands, and hence can not be 666 properly defined by functions unless some mechanism like call-by-name is added to the language. 667 Note that the definitions of ``\lstinline$&&$'' and ``\lstinline$||$'' say that they work by 668 checking that their arguments are unequal to 0, so defining ``\lstinline$!=$'' and ``\lstinline$0$'' 669 for user-defined types is enough to allow them to be used in logical expressions. 670 671 \item 672 The comma operator\index{comma expression}. It is a control-flow operator like those above. 507 ``\lstinline$?:$''. 508 These operators do not always evaluate their operands, and hence can not be properly defined by functions unless some mechanism like call-by-name is added to the language. 509 Note that the definitions of ``\lstinline$&&$'' and ``\lstinline$||$'' say that they work by checking that their arguments are unequal to 0, so defining ``\lstinline$!=$'' and ``\lstinline$0$'' for user-defined types is enough to allow them to be used in logical expressions. 510 511 \item 512 The comma operator\index{comma expression}. 513 It is a control-flow operator like those above. 673 514 Changing its meaning seems pointless and confusing. 674 515 675 516 \item 676 The ``address of'' operator. It would seem useful to define a unary ``\lstinline$&$'' operator that 677 returns values of some programmer-defined pointer-like type. The problem lies with the type of the 678 operator. Consider the expression ``\lstinline$p = &x$'', where \lstinline$x$ is of type 679 \lstinline$T$ and \lstinline$p$ has the programmer-defined type \lstinline$T_ptr$. The expression 680 might be treated as a call to the unary function ``\lstinline$&?$''. Now what is the type of the 681 function's parameter? It can not be \lstinline$T$, because then \lstinline$x$ would be passed by 682 value, and there is no way to create a useful pointer-like result from a value. Hence the parameter 683 must have type \lstinline$T *$. But then the expression must be rewritten as ``\lstinline$p = &?( &x )$'' 517 The ``address of'' operator. 518 It would seem useful to define a unary ``\lstinline$&$'' operator that returns values of some programmer-defined pointer-like type. 519 The problem lies with the type of the operator. 520 Consider the expression ``\lstinline$p = &x$'', where \lstinline$x$ is of type 521 \lstinline$T$ and \lstinline$p$ has the programmer-defined type \lstinline$T_ptr$. 522 The expression might be treated as a call to the unary function ``\lstinline$&?$''. 523 Now what is the type of the function's parameter? It can not be \lstinline$T$, because then \lstinline$x$ would be passed by value, and there is no way to create a useful pointer-like result from a value. 524 Hence the parameter must have type \lstinline$T *$. 525 But then the expression must be rewritten as ``\lstinline$p = &?( &x )$'' 684 526 ---which doesn't seem like progress! 685 527 686 The rule for address-of expressions would have to be something like ``keep applying address-of 687 functions until you get one that takes a pointer argument, then use the built-in operator and 688 stop''. It seems simpler to define a conversion function from \lstinline$T *$ to \lstinline$T_ptr$. 689 690 \item 691 The \lstinline$sizeof$ operator. It is already defined for every object type, and intimately tied 692 into the language's storage allocation model. Redefining it seems pointless. 693 694 \item 695 The ``member of'' operators ``\lstinline$.$'' and ``\lstinline$->$''. These are not really infix 696 operators, since their right ``operand'' is not a value or object. 697 698 \item 699 Cast operators\index{cast expression}. Anything that can be done with an explicit cast can be done 700 with a function call. The difference in syntax is small. 528 The rule for address-of expressions would have to be something like ``keep applying address-of functions until you get one that takes a pointer argument, then use the built-in operator and stop''. 529 It seems simpler to define a conversion function from \lstinline$T *$ to \lstinline$T_ptr$. 530 531 \item 532 The \lstinline$sizeof$ operator. 533 It is already defined for every object type, and intimately tied into the language's storage allocation model. 534 Redefining it seems pointless. 535 536 \item 537 The ``member of'' operators ``\lstinline$.$'' and ``\lstinline$->$''. 538 These are not really infix operators, since their right ``operand'' is not a value or object. 539 540 \item 541 Cast operators\index{cast expression}. 542 Anything that can be done with an explicit cast can be done with a function call. 543 The difference in syntax is small. 701 544 \end{itemize} 702 545 \end{rationale} … … 705 548 \section{Expressions} 706 549 707 \CFA allows operators and identifiers to be overloaded. Hence, each expression can have a number 708 of \define{interpretation}s, each of which has a different type. The interpretations that are 709 potentially executable are called \define{valid interpretation}s. The set of interpretations 710 depends on the kind of expression and on the interpretations of the subexpressions that it contains. 711 The rules for determining the valid interpretations of an expression are discussed below for each 712 kind of expression. Eventually the context of the outermost expression chooses one interpretation 713 of that expression. 714 715 An \define{ambiguous interpretation} is an interpretation which does not specify the exact object or 716 function denoted by every identifier in the expression. An expression can have some interpretations 717 that are ambiguous and others that are unambiguous. An expression that is chosen to be executed 718 shall not be ambiguous. 719 720 The \define{best valid interpretations} are the valid interpretations that use the fewest 721 unsafe\index{unsafe conversion} conversions. Of these, the best are those where the functions and 722 objects involved are the least polymorphic\index{less polymorphic}. Of these, the best have the 723 lowest total \Index{conversion cost}, including all implicit conversions in the argument 724 expressions. Of these, the best have the highest total conversion cost for the implicit conversions 725 (if any) applied to the argument expressions. If there is no single best valid interpretation, or if 726 the best valid interpretation is ambiguous, then the resulting interpretation is 727 ambiguous\index{ambiguous interpretation}. 728 729 \begin{rationale} 730 \CFA's rules for selecting the best interpretation are designed to allow overload resolution to 731 mimic C's operator semantics. In C, the ``usual arithmetic conversions'' are applied to the 732 operands of binary operators if necessary to convert the operands to types with a common real type. 733 In \CFA, those conversions are ``safe''. The ``fewest unsafe conversions'' rule ensures that the 734 usual conversions are done, if possible. The ``lowest total expression cost'' rule chooses the 735 proper common type. The odd-looking ``highest argument conversion cost'' rule ensures that, when 736 unary expressions must be converted, conversions of function results are preferred to conversion of 737 function arguments: \lstinline$(double)-i$ will be preferred to \lstinline$-(double)i$. 738 739 The ``least polymorphic'' rule reduces the number of polymorphic function calls, since such 740 functions are presumably more expensive than monomorphic functions and since the more specific 741 function is presumably more appropriate. It also gives preference to monomorphic values (such as the 550 \CFA allows operators and identifiers to be overloaded. 551 Hence, each expression can have a number of \define{interpretation}s, each of which has a different type. 552 The interpretations that are potentially executable are called \define{valid interpretation}s. 553 The set of interpretations depends on the kind of expression and on the interpretations of the subexpressions that it contains. 554 The rules for determining the valid interpretations of an expression are discussed below for each kind of expression. 555 Eventually the context of the outermost expression chooses one interpretation of that expression. 556 557 An \define{ambiguous interpretation} is an interpretation which does not specify the exact object or function denoted by every identifier in the expression. 558 An expression can have some interpretations that are ambiguous and others that are unambiguous. 559 An expression that is chosen to be executed shall not be ambiguous. 560 561 The \define{best valid interpretations} are the valid interpretations that use the fewest unsafe\index{unsafe conversion} conversions. 562 Of these, the best are those where the functions and objects involved are the least polymorphic\index{less polymorphic}. 563 Of these, the best have the lowest total \Index{conversion cost}, including all implicit conversions in the argument expressions. 564 Of these, the best have the highest total conversion cost for the implicit conversions 565 (if any) applied to the argument expressions. 566 If there is no single best valid interpretation, or if the best valid interpretation is ambiguous, then the resulting interpretation is ambiguous\index{ambiguous interpretation}. 567 568 \begin{rationale} 569 \CFA's rules for selecting the best interpretation are designed to allow overload resolution to mimic C's operator semantics. 570 In C, the ``usual arithmetic conversions'' are applied to the operands of binary operators if necessary to convert the operands to types with a common real type. 571 In \CFA, those conversions are ``safe''. 572 The ``fewest unsafe conversions'' rule ensures that the usual conversions are done, if possible. 573 The ``lowest total expression cost'' rule chooses the proper common type. 574 The odd-looking ``highest argument conversion cost'' rule ensures that, when unary expressions must be converted, conversions of function results are preferred to conversion of function arguments: \lstinline$(double)-i$ will be preferred to \lstinline$-(double)i$. 575 576 The ``least polymorphic'' rule reduces the number of polymorphic function calls, since such functions are presumably more expensive than monomorphic functions and since the more specific function is presumably more appropriate. 577 It also gives preference to monomorphic values (such as the 742 578 \lstinline$int$ \lstinline$0$) over polymorphic values (such as the \Index{null pointer} 743 \lstinline$0$\use{0}). However, interpretations that call polymorphic functions are preferred to 744 interpretations that perform unsafe conversions, because those conversions potentially lose accuracy 745 or violate strong typing. 579 \lstinline$0$\use{0}). 580 However, interpretations that call polymorphic functions are preferred to interpretations that perform unsafe conversions, because those conversions potentially lose accuracy or violate strong typing. 746 581 747 582 There are two notable differences between \CFA's overload resolution rules and the rules for 748 {\CC} defined in \cite{c++}. First, the result type of a function plays a role. In {\CC}, a 749 function call must be completely resolved based on the arguments to the call in most circumstances. 750 In \CFA, a function call may have several interpretations, each with a different result type, and 751 the interpretations of the containing context choose among them. Second, safe conversions are used 752 to choose among interpretations of all sorts of functions; in {\CC}, the ``usual arithmetic 753 conversions'' are a separate set of rules that apply only to the built-in operators. 754 \end{rationale} 755 756 Expressions involving certain operators\index{operator identifiers} are considered to be equivalent 757 to function calls. A transformation from ``operator'' syntax to ``function call'' syntax is defined 758 by \define{rewrite rules}. Each operator has a set of predefined functions that overload its 759 identifier. Overload resolution determines which member of the set is executed in a given 760 expression. The functions have \Index{internal linkage} and are implicitly declared with \Index{file 761 scope}. The predefined functions and rewrite rules are discussed below for each of these 762 operators. 763 \begin{rationale} 764 Predefined functions and constants have internal linkage because that simplifies optimization in 765 traditional compile-and-link environments. For instance, ``\lstinline$an_int + an_int$'' is 766 equivalent to ``\lstinline$?+?(an_int, an_int)$''. If integer addition has not been redefined in 767 the current scope, a compiler can generate code to perform the addition directly. If predefined 768 functions had external linkage, this optimization would be difficult. 769 \end{rationale} 770 771 \begin{rationale} 772 Since each subsection describes the interpretations of an expression in terms of the interpretations 773 of its subexpressions, this chapter can be taken as describing an overload resolution algorithm that 774 uses one bottom-up pass over an expression tree. Such an algorithm was first described (for Ada) by 775 Baker~\cite{Bak:overload}. It is extended here to handle polymorphic functions and arithmetic 776 conversions. The overload resolution rules and the predefined functions have been chosen so that, in 777 programs that do not introduce overloaded declarations, expressions will have the same meaning in C 778 and in \CFA. 779 \end{rationale} 780 781 \begin{rationale} 782 Expression syntax is quoted from the {\c11} standard. The syntax itself defines the precedence and 783 associativity of operators. The sections are arranged in decreasing order of precedence, with all 784 operators in a section having the same precedence. 583 {\CC} defined in \cite{C++}. 584 First, the result type of a function plays a role. 585 In {\CC}, a function call must be completely resolved based on the arguments to the call in most circumstances. 586 In \CFA, a function call may have several interpretations, each with a different result type, and the interpretations of the containing context choose among them. 587 Second, safe conversions are used to choose among interpretations of all sorts of functions; 588 in {\CC}, the ``usual arithmetic conversions'' are a separate set of rules that apply only to the built-in operators. 589 \end{rationale} 590 591 Expressions involving certain operators\index{operator identifiers} are considered to be equivalent to function calls. 592 A transformation from ``operator'' syntax to ``function call'' syntax is defined by \define{rewrite rules}. 593 Each operator has a set of predefined functions that overload its identifier. 594 Overload resolution determines which member of the set is executed in a given expression. 595 The functions have \Index{internal linkage} and are implicitly declared with \Index{file scope}. 596 The predefined functions and rewrite rules are discussed below for each of these operators. 597 \begin{rationale} 598 Predefined functions and constants have internal linkage because that simplifies optimization in traditional compile-and-link environments. 599 For instance, ``\lstinline$an_int + an_int$'' is equivalent to ``\lstinline$?+?(an_int, an_int)$''. 600 If integer addition has not been redefined in the current scope, a compiler can generate code to perform the addition directly. 601 If predefined functions had external linkage, this optimization would be difficult. 602 \end{rationale} 603 604 \begin{rationale} 605 Since each subsection describes the interpretations of an expression in terms of the interpretations of its subexpressions, this chapter can be taken as describing an overload resolution algorithm that uses one bottom-up pass over an expression tree. 606 Such an algorithm was first described (for Ada) by Baker~\cite{Bak:overload}. 607 It is extended here to handle polymorphic functions and arithmetic conversions. 608 The overload resolution rules and the predefined functions have been chosen so that, in programs that do not introduce overloaded declarations, expressions will have the same meaning in C and in \CFA. 609 \end{rationale} 610 611 \begin{rationale} 612 Expression syntax is quoted from the {\c11} standard. 613 The syntax itself defines the precedence and associativity of operators. 614 The sections are arranged in decreasing order of precedence, with all operators in a section having the same precedence. 785 615 \end{rationale} 786 616 … … 801 631 const int 1;@\use{1}@ 802 632 const int 0;@\use{0}@ 803 forall( dtype DT ) DT * const 0;804 forall( ftype FT ) FT * const 0;633 forall( dtype DT ) DT * const 0; 634 forall( ftype FT ) FT * const 0; 805 635 \end{lstlisting} 806 636 807 637 \semantics 808 The \Index{valid interpretation} of an \nonterm{identifier} are given by the visible\index{visible} 809 declarations of the identifier. 810 811 A \nonterm{constant} or \nonterm{string-literal} has one valid interpretation, which has the type 812 and value defined by {\c11}. The predefined integer identifiers ``\lstinline$1$'' and 813 ``\lstinline$0$'' have the integer values 1 and 0, respectively. The other two predefined 814 ``\lstinline$0$'' identifiers are bound to polymorphic pointer values that, when 815 specialized\index{specialization} with a data type or function type respectively, produce a null 816 pointer of that type. 638 The \Index{valid interpretation} of an \nonterm{identifier} are given by the visible\index{visible} declarations of the identifier. 639 640 A \nonterm{constant} or \nonterm{string-literal} has one valid interpretation, which has the type and value defined by {\c11}. 641 The predefined integer identifiers ``\lstinline$1$'' and ``\lstinline$0$'' have the integer values 1 and 0, respectively. 642 The other two predefined ``\lstinline$0$'' identifiers are bound to polymorphic pointer values that, when specialized\index{specialization} with a data type or function type respectively, produce a null pointer of that type. 817 643 818 644 A parenthesised expression has the same interpretations as the contained \nonterm{expression}. 819 645 820 646 \examples 821 The expression \lstinline$(void *)0$\use{0} specializes the (polymorphic) null pointer to a null 822 pointer to \lstinline$void$. \lstinline$(const void *)0$ does the same, and also uses a safe 823 conversion from \lstinline$void *$ to \lstinline$const void *$. In each case, the null pointer 824 conversion is better\index{best valid interpretations} than the unsafe conversion of the integer 647 The expression \lstinline$(void *)0$\use{0} specializes the (polymorphic) null pointer to a null pointer to \lstinline$void$. \lstinline$(const void *)0$ does the same, and also uses a safe conversion from \lstinline$void *$ to \lstinline$const void *$. 648 In each case, the null pointer conversion is better\index{best valid interpretations} than the unsafe conversion of the integer 825 649 \lstinline$0$ to a pointer. 826 650 … … 828 652 Note that the predefined identifiers have addresses. 829 653 830 \CFA does not have C's concept of ``null pointer constants'', which are not typed values but 831 special strings of tokens. The C token ``\lstinline$0$'' is an expression of type \lstinline$int$ 832 with the value ``zero'', and it \emph{also} is a null pointer constant. Similarly, 833 ``\lstinline$(void *)0$ is an expression of type \lstinline$(void *)$ whose value is a null pointer, 834 and it also is a null pointer constant. However, in C, ``\lstinline$(void *)(void *)0$'' is 835 \emph{not} a null pointer constant, even though it is null-valued, a pointer, and constant! The 836 semantics of C expressions contain many special cases to deal with subexpressions that are null 837 pointer constants. 838 839 \CFA handles these cases through overload resolution. The declaration 840 \begin{lstlisting} 841 forall( dtype DT ) DT *const 0; 842 \end{lstlisting} 843 means that \lstinline$0$ is a polymorphic object, and contains a value that can have \emph{any} 844 pointer-to-object type or pointer-to-incomplete type. The only such value is the null pointer. 845 Therefore the type \emph{alone} is enough to identify a null pointer. Where C defines an operator 846 with a special case for the null pointer constant, \CFA defines predefined functions with a 847 polymorphic object parameter. 654 \CFA does not have C's concept of ``null pointer constants'', which are not typed values but special strings of tokens. 655 The C token ``\lstinline$0$'' is an expression of type \lstinline$int$ with the value ``zero'', and it \emph{also} is a null pointer constant. 656 Similarly, 657 ``\lstinline$(void *)0$ is an expression of type \lstinline$(void *)$ whose value is a null pointer, and it also is a null pointer constant. 658 However, in C, ``\lstinline$(void *)(void *)0$'' is 659 \emph{not} a null pointer constant, even though it is null-valued, a pointer, and constant! The semantics of C expressions contain many special cases to deal with subexpressions that are null pointer constants. 660 661 \CFA handles these cases through overload resolution. 662 The declaration 663 \begin{lstlisting} 664 forall( dtype DT ) DT * const 0; 665 \end{lstlisting} means that \lstinline$0$ is a polymorphic object, and contains a value that can have \emph{any} pointer-to-object type or pointer-to-incomplete type. 666 The only such value is the null pointer. 667 Therefore the type \emph{alone} is enough to identify a null pointer. 668 Where C defines an operator with a special case for the null pointer constant, \CFA defines predefined functions with a polymorphic object parameter. 848 669 \end{rationale} 849 670 … … 851 672 \subsubsection{Generic selection} 852 673 853 \constraints The best interpretation of the controlling expression shall be 854 unambiguous\index{ambiguous interpretation}, and shall have type compatible with at most one of the 855 types named in its generic association list. If a generic selection has no \lstinline$default$ 856 generic association, the best interpretation of its controlling expression shall have type 857 compatible with exactly one of the types named in its generic association list. 674 \constraints The best interpretation of the controlling expression shall be unambiguous\index{ambiguous interpretation}, and shall have type compatible with at most one of the types named in its generic association list. 675 If a generic selection has no \lstinline$default$ generic association, the best interpretation of its controlling expression shall have type compatible with exactly one of the types named in its generic association list. 858 676 859 677 \semantics … … 883 701 \rewriterules 884 702 \begin{lstlisting} 885 a[b] @\rewrite@ ?[?]( b, a ) // if a has integer type */@\use{?[?]}@703 a[b] @\rewrite@ ?[?]( b, a ) // if a has integer type@\use{?[?]}@ 886 704 a[b] @\rewrite@ ?[?]( a, b ) // otherwise 887 a( ${\em arguments }$ ) @\rewrite@ ?()( a, ${\em arguments} )$@\use{?()}@705 a( @\emph{arguments}@ ) @\rewrite@ ?()( a, @\emph{arguments}@ )@\use{?()}@ 888 706 a++ @\rewrite@ ?++(&( a ))@\use{?++}@ 889 707 a-- @\rewrite@ ?--(&( a ))@\use{?--}@ … … 895 713 \predefined 896 714 \begin{lstlisting} 897 forall( type T ) lvalue T ?[?]( T *, ptrdiff_t );@\use{ptrdiff_t}@898 forall( type T ) lvalue _Atomic T ?[?]( _Atomic T *, ptrdiff_t );899 forall( type T ) lvalue const T ?[?]( const T *, ptrdiff_t );900 forall( type T ) lvalue restrict T ?[?]( restrict T *, ptrdiff_t );901 forall( type T ) lvalue volatile T ?[?]( volatile T *, ptrdiff_t );902 forall( type T ) lvalue _Atomic const T ?[?]( _Atomic const T *, ptrdiff_t );903 forall( type T ) lvalue _Atomic restrict T ?[?]( _Atomic restrict T *, ptrdiff_t );904 forall( type T ) lvalue _Atomic volatile T ?[?]( _Atomic volatile T *, ptrdiff_t );905 forall( type T ) lvalue const restrict T ?[?]( const restrict T *, ptrdiff_t );906 forall( type T ) lvalue const volatile T ?[?]( const volatile T *, ptrdiff_t );907 forall( type T ) lvalue restrict volatile T ?[?]( restrict volatile T *, ptrdiff_t );908 forall( type T ) lvalue _Atomic const restrict T ?[?]( _Atomic const restrict T *, ptrdiff_t );909 forall( type T ) lvalue _Atomic const volatile T ?[?]( _Atomic const volatile T *, ptrdiff_t );910 forall( type T ) lvalue _Atomic restrict volatile T ?[?]( _Atomic restrict volatile T *, ptrdiff_t );911 forall( type T ) lvalue const restrict volatile T ?[?]( const restrict volatile T *, ptrdiff_t );912 forall( type T ) lvalue _Atomic const restrict volatile T ?[?]( _Atomic const restrict volatile T *, ptrdiff_t );715 forall( otype T ) lvalue T ?[?]( T *, ptrdiff_t );@\use{ptrdiff_t}@ 716 forall( otype T ) lvalue _Atomic T ?[?]( _Atomic T *, ptrdiff_t ); 717 forall( otype T ) lvalue const T ?[?]( const T *, ptrdiff_t ); 718 forall( otype T ) lvalue restrict T ?[?]( restrict T *, ptrdiff_t ); 719 forall( otype T ) lvalue volatile T ?[?]( volatile T *, ptrdiff_t ); 720 forall( otype T ) lvalue _Atomic const T ?[?]( _Atomic const T *, ptrdiff_t ); 721 forall( otype T ) lvalue _Atomic restrict T ?[?]( _Atomic restrict T *, ptrdiff_t ); 722 forall( otype T ) lvalue _Atomic volatile T ?[?]( _Atomic volatile T *, ptrdiff_t ); 723 forall( otype T ) lvalue const restrict T ?[?]( const restrict T *, ptrdiff_t ); 724 forall( otype T ) lvalue const volatile T ?[?]( const volatile T *, ptrdiff_t ); 725 forall( otype T ) lvalue restrict volatile T ?[?]( restrict volatile T *, ptrdiff_t ); 726 forall( otype T ) lvalue _Atomic const restrict T ?[?]( _Atomic const restrict T *, ptrdiff_t ); 727 forall( otype T ) lvalue _Atomic const volatile T ?[?]( _Atomic const volatile T *, ptrdiff_t ); 728 forall( otype T ) lvalue _Atomic restrict volatile T ?[?]( _Atomic restrict volatile T *, ptrdiff_t ); 729 forall( otype T ) lvalue const restrict volatile T ?[?]( const restrict volatile T *, ptrdiff_t ); 730 forall( otype T ) lvalue _Atomic const restrict volatile T ?[?]( _Atomic const restrict volatile T *, ptrdiff_t ); 913 731 \end{lstlisting} 914 732 \semantics 915 The interpretations of subscript expressions are the interpretations of the corresponding function 916 call expressions. 733 The interpretations of subscript expressions are the interpretations of the corresponding function call expressions. 917 734 \begin{rationale} 918 735 C defines subscripting as pointer arithmetic in a way that makes \lstinline$a[i]$ and 919 \lstinline$i[a]$ equivalent. \CFA provides the equivalence through a rewrite rule to reduce the 920 number of overloadings of \lstinline$?[?]$. 921 922 Subscript expressions are rewritten as function calls that pass the first parameter by value. This 923 is somewhat unfortunate, since array-like types tend to be large. The alternative is to use the 924 rewrite rule ``\lstinline$a[b]$ \rewrite \lstinline$?[?](&(a), b)$''. However, C semantics forbid 925 this approach: the \lstinline$a$ in ``\lstinline$a[b]$'' can be an arbitrary pointer value, which 926 does not have an address. 736 \lstinline$i[a]$ equivalent. \CFA provides the equivalence through a rewrite rule to reduce the number of overloadings of \lstinline$?[?]$. 737 738 Subscript expressions are rewritten as function calls that pass the first parameter by value. 739 This is somewhat unfortunate, since array-like types tend to be large. 740 The alternative is to use the rewrite rule ``\lstinline$a[b]$ \rewrite \lstinline$?[?](&(a), b)$''. 741 However, C semantics forbid this approach: the \lstinline$a$ in ``\lstinline$a[b]$'' can be an arbitrary pointer value, which does not have an address. 927 742 928 743 The repetitive form of the predefined identifiers shows up a deficiency\index{deficiencies!pointers 929 to qualified types} of \CFA's type system. Type qualifiers are not included in type values, so 930 polymorphic functions that take pointers to arbitrary types often come in one flavor for each 931 possible qualification of the pointed-at type. 744 to qualified types} of \CFA's type system. 745 Type qualifiers are not included in type values, so polymorphic functions that take pointers to arbitrary types often come in one flavor for each possible qualification of the pointed-at type. 932 746 \end{rationale} 933 747 … … 936 750 937 751 \semantics 938 A \define{function designator} is an interpretation of an expression that has function type. The 939 \nonterm{postfix-expression} in a function call may have some interpretations that are function 940 designators and some that are not. 941 942 For those interpretations of the \nonterm{postfix-expression} that are not function designators, the 943 expression is rewritten and becomes a call of a function named ``\lstinline$?()$''. The valid 944 interpretations of the rewritten expression are determined in the manner described below. 945 946 Each combination of function designators and argument interpretations is considered. For those 947 interpretations of the \nonterm{postfix-expression} that are \Index{monomorphic function} 948 designators, the combination has a \Index{valid interpretation} if the function designator accepts 949 the number of arguments given, and each argument interpretation matches the corresponding explicit 950 parameter: 752 A \define{function designator} is an interpretation of an expression that has function type. 753 The 754 \nonterm{postfix-expression} in a function call may have some interpretations that are function designators and some that are not. 755 756 For those interpretations of the \nonterm{postfix-expression} that are not function designators, the expression is rewritten and becomes a call of a function named ``\lstinline$?()$''. 757 The valid interpretations of the rewritten expression are determined in the manner described below. 758 759 Each combination of function designators and argument interpretations is considered. 760 For those interpretations of the \nonterm{postfix-expression} that are \Index{monomorphic function} designators, the combination has a \Index{valid interpretation} if the function designator accepts the number of arguments given, and each argument interpretation matches the corresponding explicit parameter: 951 761 \begin{itemize} 952 \item 953 if the argument corresponds to a parameter in the function designator's prototype, the argument 954 interpretation must have the same type as the corresponding parameter, or be implicitly convertible 955 to the parameter's type 956 \item 957 if the function designator's type does not include a prototype or if the argument corresponds to 762 \item if the argument corresponds to a parameter in the function designator's prototype, the argument interpretation must have the same type as the corresponding parameter, or be implicitly convertible to the parameter's type 763 \item if the function designator's type does not include a prototype or if the argument corresponds to 958 764 ``\lstinline$...$'' in a prototype, a \Index{default argument promotion} is applied to it. 959 765 \end{itemize} … … 961 767 962 768 For those combinations where the interpretation of the \nonterm{postfix-expression} is a 963 \Index{polymorphic function} designator and the function designator accepts the number of arguments 964 given, there shall be at least one set of \define{implicit argument}s for the implicit parameters 965 such that 769 \Index{polymorphic function} designator and the function designator accepts the number of arguments given, there shall be at least one set of \define{implicit argument}s for the implicit parameters such that 966 770 \begin{itemize} 967 771 \item 968 If the declaration of the implicit parameter uses \Index{type-class} \lstinline$type$\use{type}, the 969 implicit argument must be an object type; if it uses \lstinline$dtype$, the implicit argument must 970 be an object type or an incomplete type; and if it uses \lstinline$ftype$, the implicit argument 971 must be a function type. 972 973 \item 974 if an explicit parameter's type uses any implicit parameters, then the corresponding explicit 975 argument must have a type that is (or can be safely converted\index{safe conversion} to) the type 976 produced by substituting the implicit arguments for the implicit parameters in the explicit 977 parameter type. 978 979 \item 980 the remaining explicit arguments must match the remaining explicit parameters, as described for 981 monomorphic function designators. 982 983 \item 984 for each \Index{assertion parameter} in the function designator's type, there must be an object or 985 function with the same identifier that is visible at the call site and whose type is compatible with 986 or can be specialized to the type of the assertion declaration. 772 If the declaration of the implicit parameter uses \Index{type-class} \lstinline$type$\use{type}, the implicit argument must be an object type; 773 if it uses \lstinline$dtype$, the implicit argument must be an object type or an incomplete type; 774 and if it uses \lstinline$ftype$, the implicit argument must be a function type. 775 776 \item if an explicit parameter's type uses any implicit parameters, then the corresponding explicit argument must have a type that is (or can be safely converted\index{safe conversion} to) the type produced by substituting the implicit arguments for the implicit parameters in the explicit parameter type. 777 778 \item the remaining explicit arguments must match the remaining explicit parameters, as described for monomorphic function designators. 779 780 \item for each \Index{assertion parameter} in the function designator's type, there must be an object or function with the same identifier that is visible at the call site and whose type is compatible with or can be specialized to the type of the assertion declaration. 987 781 \end{itemize} 988 There is a valid interpretation for each such set of implicit parameters. The type of each valid 989 interpretation is the return type of the function designator with implicit parameter values 990 substituted for the implicit arguments. 991 992 A valid interpretation is ambiguous\index{ambiguous interpretation} if the function designator or 993 any of the argument interpretations is ambiguous. 994 995 Every valid interpretation whose return type is not compatible with any other valid interpretation's 996 return type is an interpretation of the function call expression. 997 998 Every set of valid interpretations that have mutually compatible\index{compatible type} result types 999 also produces an interpretation of the function call expression. The type of the interpretation is 1000 the \Index{composite type} of the types of the valid interpretations, and the value of the 1001 interpretation is that of the \Index{best valid interpretation}. 1002 \begin{rationale} 1003 One desirable property of a polymorphic programming language is \define{generalizability}: the 1004 ability to replace an abstraction with a more general but equivalent abstraction without requiring 1005 changes in any of the uses of the original\cite{Cormack90}. For instance, it should be possible to 1006 replace a function ``\lstinline$int f( int );$'' with ``\lstinline$forall( type T ) T f( T );$'' 1007 without affecting any calls of \lstinline$f$. 782 There is a valid interpretation for each such set of implicit parameters. 783 The type of each valid interpretation is the return type of the function designator with implicit parameter values substituted for the implicit arguments. 784 785 A valid interpretation is ambiguous\index{ambiguous interpretation} if the function designator or any of the argument interpretations is ambiguous. 786 787 Every valid interpretation whose return type is not compatible with any other valid interpretation's return type is an interpretation of the function call expression. 788 789 Every set of valid interpretations that have mutually compatible\index{compatible type} result types also produces an interpretation of the function call expression. 790 The type of the interpretation is the \Index{composite type} of the types of the valid interpretations, and the value of the interpretation is that of the \Index{best valid interpretation}. 791 \begin{rationale} 792 One desirable property of a polymorphic programming language is \define{generalizability}: the ability to replace an abstraction with a more general but equivalent abstraction without requiring changes in any of the uses of the original\cite{Cormack90}. 793 For instance, it should be possible to replace a function ``\lstinline$int f( int );$'' with ``\lstinline$forall( otype T ) T f( T );$'' without affecting any calls of \lstinline$f$. 1008 794 1009 795 \CFA\index{deficiencies!generalizability} does not fully possess this property, because … … 1015 801 float f; 1016 802 double d; 1017 f = g( f, f ); // (1) 1018 f = g( i, f ); // (2) (safe conversion to float) 1019 f = g( d, f ); // (3) (unsafe conversion to float) 1020 \end{lstlisting} 1021 If \lstinline$g$ was replaced by ``\lstinline$forall( type T ) T g( T, T );$'', the first and second 1022 calls would be unaffected, but the third would change: \lstinline$f$ would be converted to 803 f = g( f, f ); // (1) 804 f = g( i, f ); // (2) (safe conversion to float) 805 f = g( d, f ); // (3) (unsafe conversion to float) 806 \end{lstlisting} 807 If \lstinline$g$ was replaced by ``\lstinline$forall( otype T ) T g( T, T );$'', the first and second calls would be unaffected, but the third would change: \lstinline$f$ would be converted to 1023 808 \lstinline$double$, and the result would be a \lstinline$double$. 1024 809 1025 Another example is the function ``\lstinline$void h( int *);$''. This function can be passed a1026 \lstinline$void *$ argument, but the generalization ``\lstinline$forall( type T ) void h( T *);$'' 1027 can not. In this case, \lstinline$void$ is not a valid value for \lstinline$T$ because it is not an 1028 object type. If unsafe conversions were allowed, \lstinline$T$ could be inferred to be \emph{any} 1029 object type, which is undesirable.810 Another example is the function ``\lstinline$void h( int *);$''. 811 This function can be passed a 812 \lstinline$void *$ argument, but the generalization ``\lstinline$forall( otype T ) void h( T *);$'' can not. 813 In this case, \lstinline$void$ is not a valid value for \lstinline$T$ because it is not an object type. 814 If unsafe conversions were allowed, \lstinline$T$ could be inferred to be \emph{any} object type, which is undesirable. 1030 815 \end{rationale} 1031 816 … … 1033 818 A function called ``\lstinline$?()$'' might be part of a numerical differentiation package. 1034 819 \begin{lstlisting} 1035 extern type Derivative;820 extern otype Derivative; 1036 821 extern double ?()( Derivative, double ); 1037 822 extern Derivative derivative_of( double (*f)( double ) ); … … 1045 830 For that interpretation, the function call is treated as ``\lstinline$?()( sin_dx, 12.9 )$''. 1046 831 \begin{lstlisting} 1047 int f( long ); // (1) 1048 int f( int, int ); // (2) 832 int f( long ); // (1) 833 int f( int, int ); // (2) 1049 834 int f( int *); // (3) 1050 1051 835 int i = f( 5 ); // calls (1) 1052 836 \end{lstlisting} 1053 Function (1) provides a valid interpretation of ``\lstinline$f( 5 )$'', using an implicit 1054 \lstinline$int$ to \lstinline$long$ conversion. The other functions do not, since the second 1055 requires two arguments, and since there is no implicit conversion from \lstinline$int$ to 1056 \lstinline$int *$ that could be used with the third function. 1057 1058 \begin{lstlisting} 1059 forall( type T ) T h( T ); 837 Function (1) provides a valid interpretation of ``\lstinline$f( 5 )$'', using an implicit \lstinline$int$ to \lstinline$long$ conversion. 838 The other functions do not, since the second requires two arguments, and since there is no implicit conversion from \lstinline$int$ to \lstinline$int *$ that could be used with the third function. 839 840 \begin{lstlisting} 841 forall( otype T ) T h( T ); 1060 842 double d = h( 1.5 ); 1061 843 \end{lstlisting} … … 1064 846 1065 847 \begin{lstlisting} 1066 forall( type T, type U ) void g( T, U ); // (4)1067 forall( type T ) void g( T, T ); // (5)1068 forall( type T ) void g( T, long ); // (6)1069 void g( long, long ); // (7) 848 forall( otype T, otype U ) void g( T, U ); // (4) 849 forall( otype T ) void g( T, T ); // (5) 850 forall( otype T ) void g( T, long ); // (6) 851 void g( long, long ); // (7) 1070 852 double d; 1071 853 int i; 1072 854 int *p; 1073 1074 g( d, d ); // calls (5) 1075 g( d, i ); // calls (6) 1076 g( i, i ); // calls (7) 855 g( d, d ); // calls (5) 856 g( d, i ); // calls (6) 857 g( i, i ); // calls (7) 1077 858 g( i, p ); // calls (4) 1078 859 \end{lstlisting} 1079 The first call has valid interpretations for all four versions of \lstinline$g$. (6) and (7) are 1080 discarded because they involve unsafe \lstinline$double$-to-\lstinline$long$ conversions. (5) is 1081 chosen because it is less polymorphic than (4). 1082 1083 For the second call, (7) is again discarded. Of the remaining interpretations for (4), (5), and (6) 1084 (with \lstinline$i$ converted to \lstinline$long$), (6) is chosen because it is the least 1085 polymorphic. 1086 1087 The third call has valid interpretations for all of the functions; (7) is chosen since it is not 1088 polymorphic at all. 1089 1090 The fourth call has no interpretation for (5), because its arguments must have compatible type. (4) 1091 is chosen because it does not involve unsafe conversions. 1092 \begin{lstlisting} 1093 forall( type T ) T min( T, T ); 860 The first call has valid interpretations for all four versions of \lstinline$g$. (6) and (7) are discarded because they involve unsafe \lstinline$double$-to-\lstinline$long$ conversions. (5) is chosen because it is less polymorphic than (4). 861 862 For the second call, (7) is again discarded. 863 Of the remaining interpretations for (4), (5), and (6) (with \lstinline$i$ converted to \lstinline$long$), (6) is chosen because it is the least polymorphic. 864 865 The third call has valid interpretations for all of the functions; 866 (7) is chosen since it is not polymorphic at all. 867 868 The fourth call has no interpretation for (5), because its arguments must have compatible type. (4) is chosen because it does not involve unsafe conversions. 869 \begin{lstlisting} 870 forall( otype T ) T min( T, T ); 1094 871 double max( double, double ); 1095 context min_max( T ) {@\impl{min_max}@872 trait min_max( T ) {@\impl{min_max}@ 1096 873 T min( T, T ); 1097 874 T max( T, T ); 1098 875 } 1099 forall( type U | min_max( U ) ) void shuffle( U, U ); 1100 shuffle(9, 10); 1101 \end{lstlisting} 1102 The only possibility for \lstinline$U$ is \lstinline$double$, because that is the type used in the 1103 only visible \lstinline$max$ function. 9 and 10 must be converted to \lstinline$double$, and 876 forall( otype U | min_max( U ) ) void shuffle( U, U ); 877 shuffle( 9, 10 ); 878 \end{lstlisting} 879 The only possibility for \lstinline$U$ is \lstinline$double$, because that is the type used in the only visible \lstinline$max$ function. 9 and 10 must be converted to \lstinline$double$, and 1104 880 \lstinline$min$ must be specialized with \lstinline$T$ bound to \lstinline$double$. 1105 881 \begin{lstlisting} 1106 extern void q( int ); // (8) 1107 extern void q( void * ); // (9) 882 extern void q( int ); // (8) 883 extern void q( void * ); // (9) 1108 884 extern void r(); 1109 885 q( 0 ); 1110 886 r( 0 ); 1111 887 \end{lstlisting} 1112 The \lstinline$int 0$ could be passed to (8), or the \lstinline$(void *)$ \Index{specialization} of 1113 the null pointer\index{null pointer} \lstinline$0$\use{0} could be passed to (9). The former is 1114 chosen because the \lstinline$int$ \lstinline$0$ is \Index{less polymorphic}. For 1115 the same reason, \lstinline$int$ \lstinline$0$ is passed to \lstinline$r()$, even though it has 1116 \emph{no} declared parameter types. 888 The \lstinline$int 0$ could be passed to (8), or the \lstinline$(void *)$ \Index{specialization} of the null pointer\index{null pointer} \lstinline$0$\use{0} could be passed to (9). 889 The former is chosen because the \lstinline$int$ \lstinline$0$ is \Index{less polymorphic}. 890 For the same reason, \lstinline$int$ \lstinline$0$ is passed to \lstinline$r()$, even though it has \emph{no} declared parameter types. 1117 891 1118 892 1119 893 \subsubsection{Structure and union members} 1120 894 1121 \semantics In the member selection expression ``\lstinline$s$.\lstinline$m$'', there shall be at 1122 least one interpretation of \lstinline$s$ whose type is a structure type or union type containing a 1123 member named \lstinline$m$. If two or more interpretations of \lstinline$s$ have members named 1124 \lstinline$m$ with mutually compatible types, then the expression has an \Index{ambiguous 1125 interpretation} whose type is the composite type of the types of the members. If an interpretation 1126 of \lstinline$s$ has a member \lstinline$m$ whose type is not compatible with any other 1127 \lstinline$s$'s \lstinline$m$, then the expression has an interpretation with the member's type. The 1128 expression has no other interpretations. 895 \semantics In the member selection expression ``\lstinline$s$.\lstinline$m$'', there shall be at least one interpretation of \lstinline$s$ whose type is a structure type or union type containing a member named \lstinline$m$. 896 If two or more interpretations of \lstinline$s$ have members named 897 \lstinline$m$ with mutually compatible types, then the expression has an \Index{ambiguous interpretation} whose type is the composite type of the types of the members. 898 If an interpretation of \lstinline$s$ has a member \lstinline$m$ whose type is not compatible with any other 899 \lstinline$s$'s \lstinline$m$, then the expression has an interpretation with the member's type. 900 The expression has no other interpretations. 1129 901 1130 902 The expression ``\lstinline$p->m$'' has the same interpretations as the expression … … 1136 908 \predefined 1137 909 \begin{lstlisting} 1138 _Bool ?++( volatile _Bool * ), 1139 ?++( _Atomic volatile _Bool * ); 1140 char ?++( volatile char * ), 1141 ?++( _Atomic volatile char * ); 1142 signed char ?++( volatile signed char * ), 1143 ?++( _Atomic volatile signed char * ); 1144 unsigned char ?++( volatile signed char * ), 1145 ?++( _Atomic volatile signed char * ); 1146 short int ?++( volatile short int * ), 1147 ?++( _Atomic volatile short int * ); 1148 unsigned short int ?++( volatile unsigned short int * ), 1149 ?++( _Atomic volatile unsigned short int * ); 1150 int ?++( volatile int * ), 1151 ?++( _Atomic volatile int * ); 1152 unsigned int ?++( volatile unsigned int * ), 1153 ?++( _Atomic volatile unsigned int * ); 1154 long int ?++( volatile long int * ), 1155 ?++( _Atomic volatile long int * ); 1156 long unsigned int ?++( volatile long unsigned int * ), 1157 ?++( _Atomic volatile long unsigned int * ); 1158 long long int ?++( volatile long long int * ), 1159 ?++( _Atomic volatile long long int * ); 1160 long long unsigned ?++( volatile long long unsigned int * ), 1161 ?++( _Atomic volatile long long unsigned int * ); 1162 float ?++( volatile float * ), 1163 ?++( _Atomic volatile float * ); 1164 double ?++( volatile double * ), 1165 ?++( _Atomic volatile double * ); 1166 long double ?++( volatile long double * ), 1167 ?++( _Atomic volatile long double * ); 1168 1169 forall( type T ) T * ?++( T * restrict volatile * ), 1170 * ?++( T * _Atomic restrict volatile * ); 1171 1172 forall( type T ) _Atomic T * ?++( _Atomic T * restrict volatile * ), 1173 * ?++( _Atomic T * _Atomic restrict volatile * ); 1174 1175 forall( type T ) const T * ?++( const T * restrict volatile * ), 1176 * ?++( const T * _Atomic restrict volatile * ); 1177 1178 forall( type T ) volatile T * ?++( volatile T * restrict volatile * ), 1179 * ?++( volatile T * _Atomic restrict volatile * ); 1180 1181 forall( type T ) restrict T * ?++( restrict T * restrict volatile * ), 1182 * ?++( restrict T * _Atomic restrict volatile * ); 1183 1184 forall( type T ) _Atomic const T * ?++( _Atomic const T * restrict volatile * ), 910 _Bool ?++( volatile _Bool * ), ?++( _Atomic volatile _Bool * ); 911 char ?++( volatile char * ), ?++( _Atomic volatile char * ); 912 signed char ?++( volatile signed char * ), ?++( _Atomic volatile signed char * ); 913 unsigned char ?++( volatile signed char * ), ?++( _Atomic volatile signed char * ); 914 short int ?++( volatile short int * ), ?++( _Atomic volatile short int * ); 915 unsigned short int ?++( volatile unsigned short int * ), ?++( _Atomic volatile unsigned short int * ); 916 int ?++( volatile int * ), ?++( _Atomic volatile int * ); 917 unsigned int ?++( volatile unsigned int * ), ?++( _Atomic volatile unsigned int * ); 918 long int ?++( volatile long int * ), ?++( _Atomic volatile long int * ); 919 long unsigned int ?++( volatile long unsigned int * ), ?++( _Atomic volatile long unsigned int * ); 920 long long int ?++( volatile long long int * ), ?++( _Atomic volatile long long int * ); 921 long long unsigned ?++( volatile long long unsigned int * ), ?++( _Atomic volatile long long unsigned int * ); 922 float ?++( volatile float * ), ?++( _Atomic volatile float * ); 923 double ?++( volatile double * ), ?++( _Atomic volatile double * ); 924 long double ?++( volatile long double * ), ?++( _Atomic volatile long double * ); 925 926 forall( otype T ) T * ?++( T * restrict volatile * ), * ?++( T * _Atomic restrict volatile * ); 927 forall( otype T ) _Atomic T * ?++( _Atomic T * restrict volatile * ), * ?++( _Atomic T * _Atomic restrict volatile * ); 928 forall( otype T ) const T * ?++( const T * restrict volatile * ), * ?++( const T * _Atomic restrict volatile * ); 929 forall( otype T ) volatile T * ?++( volatile T * restrict volatile * ), * ?++( volatile T * _Atomic restrict volatile * ); 930 forall( otype T ) restrict T * ?++( restrict T * restrict volatile * ), * ?++( restrict T * _Atomic restrict volatile * ); 931 forall( otype T ) _Atomic const T * ?++( _Atomic const T * restrict volatile * ), 1185 932 * ?++( _Atomic const T * _Atomic restrict volatile * ); 1186 1187 forall( type T ) _Atomic restrict T * ?++( _Atomic restrict T * restrict volatile * ), 933 forall( otype T ) _Atomic restrict T * ?++( _Atomic restrict T * restrict volatile * ), 1188 934 * ?++( _Atomic restrict T * _Atomic restrict volatile * ); 1189 1190 forall( type T ) _Atomic volatile T * ?++( _Atomic volatile T * restrict volatile * ), 935 forall( otype T ) _Atomic volatile T * ?++( _Atomic volatile T * restrict volatile * ), 1191 936 * ?++( _Atomic volatile T * _Atomic restrict volatile * ); 1192 1193 forall( type T ) const restrict T * ?++( const restrict T * restrict volatile * ), 937 forall( otype T ) const restrict T * ?++( const restrict T * restrict volatile * ), 1194 938 * ?++( const restrict T * _Atomic restrict volatile * ); 1195 1196 forall( type T ) const volatile T * ?++( const volatile T * restrict volatile * ), 939 forall( otype T ) const volatile T * ?++( const volatile T * restrict volatile * ), 1197 940 * ?++( const volatile T * _Atomic restrict volatile * ); 1198 1199 forall( type T ) restrict volatile T * ?++( restrict volatile T * restrict volatile * ), 941 forall( otype T ) restrict volatile T * ?++( restrict volatile T * restrict volatile * ), 1200 942 * ?++( restrict volatile T * _Atomic restrict volatile * ); 1201 1202 forall( type T ) _Atomic const restrict T * ?++( _Atomic const restrict T * restrict volatile * ), 943 forall( otype T ) _Atomic const restrict T * ?++( _Atomic const restrict T * restrict volatile * ), 1203 944 * ?++( _Atomic const restrict T * _Atomic restrict volatile * ); 1204 1205 forall( type T ) _Atomic const volatile T * ?++( _Atomic const volatile T * restrict volatile * ), 945 forall( otype T ) _Atomic const volatile T * ?++( _Atomic const volatile T * restrict volatile * ), 1206 946 * ?++( _Atomic const volatile T * _Atomic restrict volatile * ); 1207 1208 forall( type T ) _Atomic restrict volatile T * ?++( _Atomic restrict volatile T * restrict volatile * ), 947 forall( otype T ) _Atomic restrict volatile T * ?++( _Atomic restrict volatile T * restrict volatile * ), 1209 948 * ?++( _Atomic restrict volatile T * _Atomic restrict volatile * ); 1210 1211 forall( type T ) const restrict volatile T * ?++( const restrict volatile T * restrict volatile * ), 949 forall( otype T ) const restrict volatile T * ?++( const restrict volatile T * restrict volatile * ), 1212 950 * ?++( const restrict volatile T * _Atomic restrict volatile * ); 1213 1214 forall( type T ) _Atomic const restrict volatile T * ?++( _Atomic const restrict volatile T * restrict volatile * ), 951 forall( otype T ) _Atomic const restrict volatile T * ?++( _Atomic const restrict volatile T * restrict volatile * ), 1215 952 * ?++( _Atomic const restrict volatile T * _Atomic restrict volatile * ); 1216 953 1217 _Bool ?--( volatile _Bool * ), 1218 ?--( _Atomic volatile _Bool * ); 1219 char ?--( volatile char * ), 1220 ?--( _Atomic volatile char * ); 1221 signed char ?--( volatile signed char * ), 1222 ?--( _Atomic volatile signed char * ); 1223 unsigned char ?--( volatile signed char * ), 1224 ?--( _Atomic volatile signed char * ); 1225 short int ?--( volatile short int * ), 1226 ?--( _Atomic volatile short int * ); 1227 unsigned short int ?--( volatile unsigned short int * ), 1228 ?--( _Atomic volatile unsigned short int * ); 1229 int ?--( volatile int * ), 1230 ?--( _Atomic volatile int * ); 1231 unsigned int ?--( volatile unsigned int * ), 1232 ?--( _Atomic volatile unsigned int * ); 1233 long int ?--( volatile long int * ), 1234 ?--( _Atomic volatile long int * ); 1235 long unsigned int ?--( volatile long unsigned int * ), 1236 ?--( _Atomic volatile long unsigned int * ); 1237 long long int ?--( volatile long long int * ), 1238 ?--( _Atomic volatile long long int * ); 1239 long long unsigned ?--( volatile long long unsigned int * ), 1240 ?--( _Atomic volatile long long unsigned int * ); 1241 float ?--( volatile float * ), 1242 ?--( _Atomic volatile float * ); 1243 double ?--( volatile double * ), 1244 ?--( _Atomic volatile double * ); 1245 long double ?--( volatile long double * ), 1246 ?--( _Atomic volatile long double * ); 1247 1248 forall( type T ) T * ?--( T * restrict volatile * ), 1249 * ?--( T * _Atomic restrict volatile * ); 1250 1251 forall( type T ) _Atomic T * ?--( _Atomic T * restrict volatile * ), 1252 * ?--( _Atomic T * _Atomic restrict volatile * ); 1253 1254 forall( type T ) const T * ?--( const T * restrict volatile * ), 1255 * ?--( const T * _Atomic restrict volatile * ); 1256 1257 forall( type T ) volatile T * ?--( volatile T * restrict volatile * ), 1258 * ?--( volatile T * _Atomic restrict volatile * ); 1259 1260 forall( type T ) restrict T * ?--( restrict T * restrict volatile * ), 1261 * ?--( restrict T * _Atomic restrict volatile * ); 1262 1263 forall( type T ) _Atomic const T * ?--( _Atomic const T * restrict volatile * ), 954 _Bool ?--( volatile _Bool * ), ?--( _Atomic volatile _Bool * ); 955 char ?--( volatile char * ), ?--( _Atomic volatile char * ); 956 signed char ?--( volatile signed char * ), ?--( _Atomic volatile signed char * ); 957 unsigned char ?--( volatile signed char * ), ?--( _Atomic volatile signed char * ); 958 short int ?--( volatile short int * ), ?--( _Atomic volatile short int * ); 959 unsigned short int ?--( volatile unsigned short int * ), ?--( _Atomic volatile unsigned short int * ); 960 int ?--( volatile int * ), ?--( _Atomic volatile int * ); 961 unsigned int ?--( volatile unsigned int * ), ?--( _Atomic volatile unsigned int * ); 962 long int ?--( volatile long int * ), ?--( _Atomic volatile long int * ); 963 long unsigned int ?--( volatile long unsigned int * ), ?--( _Atomic volatile long unsigned int * ); 964 long long int ?--( volatile long long int * ), ?--( _Atomic volatile long long int * ); 965 long long unsigned ?--( volatile long long unsigned int * ), ?--( _Atomic volatile long long unsigned int * ); 966 float ?--( volatile float * ), ?--( _Atomic volatile float * ); 967 double ?--( volatile double * ), ?--( _Atomic volatile double * ); 968 long double ?--( volatile long double * ), ?--( _Atomic volatile long double * ); 969 970 forall( otype T ) T * ?--( T * restrict volatile * ), * ?--( T * _Atomic restrict volatile * ); 971 forall( otype T ) _Atomic T * ?--( _Atomic T * restrict volatile * ), * ?--( _Atomic T * _Atomic restrict volatile * ); 972 forall( otype T ) const T * ?--( const T * restrict volatile * ), * ?--( const T * _Atomic restrict volatile * ); 973 forall( otype T ) volatile T * ?--( volatile T * restrict volatile * ), * ?--( volatile T * _Atomic restrict volatile * ); 974 forall( otype T ) restrict T * ?--( restrict T * restrict volatile * ), * ?--( restrict T * _Atomic restrict volatile * ); 975 forall( otype T ) _Atomic const T * ?--( _Atomic const T * restrict volatile * ), 1264 976 * ?--( _Atomic const T * _Atomic restrict volatile * ); 1265 1266 forall( type T ) _Atomic restrict T * ?--( _Atomic restrict T * restrict volatile * ), 977 forall( otype T ) _Atomic restrict T * ?--( _Atomic restrict T * restrict volatile * ), 1267 978 * ?--( _Atomic restrict T * _Atomic restrict volatile * ); 1268 1269 forall( type T ) _Atomic volatile T * ?--( _Atomic volatile T * restrict volatile * ), 979 forall( otype T ) _Atomic volatile T * ?--( _Atomic volatile T * restrict volatile * ), 1270 980 * ?--( _Atomic volatile T * _Atomic restrict volatile * ); 1271 1272 forall( type T ) const restrict T * ?--( const restrict T * restrict volatile * ), 981 forall( otype T ) const restrict T * ?--( const restrict T * restrict volatile * ), 1273 982 * ?--( const restrict T * _Atomic restrict volatile * ); 1274 1275 forall( type T ) const volatile T * ?--( const volatile T * restrict volatile * ), 983 forall( otype T ) const volatile T * ?--( const volatile T * restrict volatile * ), 1276 984 * ?--( const volatile T * _Atomic restrict volatile * ); 1277 1278 forall( type T ) restrict volatile T * ?--( restrict volatile T * restrict volatile * ), 985 forall( otype T ) restrict volatile T * ?--( restrict volatile T * restrict volatile * ), 1279 986 * ?--( restrict volatile T * _Atomic restrict volatile * ); 1280 1281 forall( type T ) _Atomic const restrict T * ?--( _Atomic const restrict T * restrict volatile * ), 987 forall( otype T ) _Atomic const restrict T * ?--( _Atomic const restrict T * restrict volatile * ), 1282 988 * ?--( _Atomic const restrict T * _Atomic restrict volatile * ); 1283 1284 forall( type T ) _Atomic const volatile T * ?--( _Atomic const volatile T * restrict volatile * ), 989 forall( otype T ) _Atomic const volatile T * ?--( _Atomic const volatile T * restrict volatile * ), 1285 990 * ?--( _Atomic const volatile T * _Atomic restrict volatile * ); 1286 1287 forall( type T ) _Atomic restrict volatile T * ?--( _Atomic restrict volatile T * restrict volatile * ), 991 forall( otype T ) _Atomic restrict volatile T * ?--( _Atomic restrict volatile T * restrict volatile * ), 1288 992 * ?--( _Atomic restrict volatile T * _Atomic restrict volatile * ); 1289 1290 forall( type T ) const restrict volatile T * ?--( const restrict volatile T * restrict volatile * ), 993 forall( otype T ) const restrict volatile T * ?--( const restrict volatile T * restrict volatile * ), 1291 994 * ?--( const restrict volatile T * _Atomic restrict volatile * ); 1292 1293 forall( type T ) _Atomic const restrict volatile T * ?--( _Atomic const restrict volatile T * restrict volatile * ), 995 forall( otype T ) _Atomic const restrict volatile T * ?--( _Atomic const restrict volatile T * restrict volatile * ), 1294 996 * ?--( _Atomic const restrict volatile T * _Atomic restrict volatile * ); 1295 997 \end{lstlisting} … … 1308 1010 1309 1011 \begin{rationale} 1310 Note that ``\lstinline$++$'' and ``\lstinline$--$'' are rewritten as function calls that are given a 1311 pointer to that operand. (This is true of all operators that modify an operand.) As Hamish Macdonald 1312 has pointed out, this forces the modified operand of such expressions to be an lvalue. This 1313 partially enforces the C semantic rule that such operands must be \emph{modifiable} lvalues. 1314 \end{rationale} 1315 1316 \begin{rationale} 1317 In C, a semantic rule requires that pointer operands of increment and decrement be pointers to 1318 object types. Hence, \lstinline$void *$ objects cannot be incremented. In \CFA, the restriction 1319 follows from the use of a \lstinline$type$ parameter in the predefined function definitions, as 1320 opposed to \lstinline$dtype$, since only object types can be inferred arguments corresponding to the 1321 type parameter \lstinline$T$. 1012 Note that ``\lstinline$++$'' and ``\lstinline$--$'' are rewritten as function calls that are given a pointer to that operand. (This is true of all operators that modify an operand.) As Hamish Macdonald has pointed out, this forces the modified operand of such expressions to be an lvalue. 1013 This partially enforces the C semantic rule that such operands must be \emph{modifiable} lvalues. 1014 \end{rationale} 1015 1016 \begin{rationale} 1017 In C, a semantic rule requires that pointer operands of increment and decrement be pointers to object types. 1018 Hence, \lstinline$void *$ objects cannot be incremented. 1019 In \CFA, the restriction follows from the use of a \lstinline$type$ parameter in the predefined function definitions, as opposed to \lstinline$dtype$, since only object types can be inferred arguments corresponding to the type parameter \lstinline$T$. 1322 1020 \end{rationale} 1323 1021 1324 1022 \semantics 1325 First, each interpretation of the operand of an increment or decrement expression is considered 1326 separately. For each interpretation that is a bit-field or is declared with the 1327 \lstinline$register$\index{register@{\lstinline$register$}} \index{Itorage-class specifier}, the 1328 expression has one valid interpretation, with the type of the operand, and the expression is 1329 ambiguous if the operand is. 1330 1331 For the remaining interpretations, the expression is rewritten, and the interpretations of the 1332 expression are the interpretations of the corresponding function call. Finally, all interpretations 1333 of the expression produced for the different interpretations of the operand are combined to produce 1334 the interpretations of the expression as a whole; where interpretations have compatible result 1335 types, the best interpretations are selected in the manner described for function call expressions. 1023 First, each interpretation of the operand of an increment or decrement expression is considered separately. 1024 For each interpretation that is a bit-field or is declared with the 1025 \lstinline$register$\index{register@{\lstinline$register$}} \index{Itorage-class specifier}, the expression has one valid interpretation, with the type of the operand, and the expression is ambiguous if the operand is. 1026 1027 For the remaining interpretations, the expression is rewritten, and the interpretations of the expression are the interpretations of the corresponding function call. 1028 Finally, all interpretations of the expression produced for the different interpretations of the operand are combined to produce the interpretations of the expression as a whole; where interpretations have compatible result types, the best interpretations are selected in the manner described for function call expressions. 1336 1029 1337 1030 \examples … … 1346 1039 \lstinline$vs++$ calls the \lstinline$?++$ function with the \lstinline$volatile short *$ parameter. 1347 1040 \lstinline$s++$ does the same, applying the safe conversion from \lstinline$short int *$ to 1348 \lstinline$volatile short int *$. Note that there is no conversion that adds an \lstinline$_Atomic$ 1349 qualifier, so the \lstinline$_Atomic volatile short int$ overloading does not provide a valid 1350 interpretation. 1041 \lstinline$volatile short int *$. 1042 Note that there is no conversion that adds an \lstinline$_Atomic$ qualifier, so the \lstinline$_Atomic volatile short int$ overloading does not provide a valid interpretation. 1351 1043 \end{sloppypar} 1352 1044 1353 There is no safe conversion from \lstinline$const short int *$ to \lstinline$volatile short int *$, 1354 and no \lstinline$?++$ function that accepts a \lstinline$const *$ parameter, so \lstinline$cs++$ 1355 has no valid interpretations. 1356 1357 The best valid interpretation of \lstinline$as++$ calls the \lstinline$short ?++$ function with the 1358 \lstinline$_Atomic volatile short int *$ parameter, applying a safe conversion to add the 1359 \lstinline$volatile$ qualifier. 1360 1361 \begin{lstlisting} 1362 char * const restrict volatile * restrict volatile pqpc; pqpc++ 1363 char * * restrict volatile ppc; ppc++; 1364 \end{lstlisting} 1365 Since \lstinline$&(pqpc)$ has type \lstinline$char * const restrict volatile * restrict volatile *$, 1366 the best valid interpretation of \lstinline$pqpc++$ calls the polymorphic \lstinline$?++$ function 1367 with the \lstinline$const restrict volatile T * restrict volatile *$ parameter, inferring 1368 \lstinline$T$ to be \lstinline$char *$. 1369 1370 \begin{sloppypar} 1371 \lstinline$ppc++$ calls the same function, again inferring \lstinline$T$ to be \lstinline$char *$, 1372 and using the safe conversions from \lstinline$T$ to \lstinline$T const restrict volatile$. 1373 \end{sloppypar} 1374 1375 \begin{rationale} 1376 Increment and decrement expressions show up a deficiency of \CFA's type system. There is no such 1377 thing as a pointer to a register object or bit-field\index{deficiencies!pointers to bit-fields}. 1378 Therefore, there is no way to define a function that alters them, and hence no way to define 1379 increment and decrement functions for them. As a result, the semantics of increment and decrement 1380 expressions must treat them specially. This holds true for all of the operators that may modify 1381 such objects. 1382 \end{rationale} 1383 1384 \begin{rationale} 1385 The polymorphic overloadings for pointer increment and decrement can be understood by considering 1386 increasingly complex types. 1045 There is no safe conversion from \lstinline$const short int *$ to \lstinline$volatile short int *$, and no \lstinline$?++$ function that accepts a \lstinline$const *$ parameter, so \lstinline$cs++$ has no valid interpretations. 1046 1047 The best valid interpretation of \lstinline$as++$ calls the \lstinline$short ?++$ function with the \lstinline$_Atomic volatile short int *$ parameter, applying a safe conversion to add the \lstinline$volatile$ qualifier. 1048 \begin{lstlisting} 1049 char * const restrict volatile * restrict volatile pqpc; 1050 pqpc++ 1051 char * * restrict volatile ppc; 1052 ppc++; 1053 \end{lstlisting} 1054 Since \lstinline$&(pqpc)$ has type \lstinline$char * const restrict volatile * restrict volatile *$, the best valid interpretation of \lstinline$pqpc++$ calls the polymorphic \lstinline$?++$ function with the \lstinline$const restrict volatile T * restrict volatile *$ parameter, inferring \lstinline$T$ to be \lstinline$char *$. 1055 1056 \lstinline$ppc++$ calls the same function, again inferring \lstinline$T$ to be \lstinline$char *$, and using the safe conversions from \lstinline$T$ to \lstinline$T const$ \lstinline$restrict volatile$. 1057 1058 \begin{rationale} 1059 Increment and decrement expressions show up a deficiency of \CFA's type system. 1060 There is no such thing as a pointer to a register object or bit-field\index{deficiencies!pointers to bit-fields}. 1061 Therefore, there is no way to define a function that alters them, and hence no way to define increment and decrement functions for them. 1062 As a result, the semantics of increment and decrement expressions must treat them specially. 1063 This holds true for all of the operators that may modify such objects. 1064 \end{rationale} 1065 1066 \begin{rationale} 1067 The polymorphic overloadings for pointer increment and decrement can be understood by considering increasingly complex types. 1387 1068 \begin{enumerate} 1388 1069 \item 1389 ``\lstinline$char * p; p++;$''. The argument to \lstinline$?++$ has type \lstinline$char * *$, and 1390 the result has type \lstinline$char *$. The expression would be valid if \lstinline$?++$ were 1391 declared by 1392 \begin{lstlisting} 1393 forall( type T ) T * ?++( T * * ); 1394 \end{lstlisting} 1395 with \lstinline$T$ inferred to be \lstinline$char$. 1396 1397 \item 1398 ``\lstinline$char *restrict volatile qp; qp++$''. The result again has type \lstinline$char *$, but 1399 the argument now has type \lstinline$char *restrict volatile *$, so it cannot be passed to the 1400 hypothetical function declared in point 1. Hence the actual predefined function is 1401 \begin{lstlisting} 1402 forall( type T ) T * ?++( T * restrict volatile * ); 1403 \end{lstlisting} 1404 which also accepts a \lstinline$char * *$ argument, because of the safe conversions that add 1405 \lstinline$volatile$ and \lstinline$restrict$ qualifiers. (The parameter is not const-qualified, so 1406 constant pointers cannot be incremented.) 1407 1408 \item 1409 ``\lstinline$char *_Atomic ap; ap++$''. The result again has type \lstinline$char *$, but no safe 1410 conversion adds an \lstinline$_Atomic$ qualifier, so the function in point 2 is not applicable. A 1411 separate overloading of \lstinline$?++$ is required. 1412 1413 \item 1414 ``\lstinline$char const volatile * pq; pq++$''. Here the result has type 1070 ``\lstinline$char * p; p++;$''. 1071 The argument to \lstinline$?++$ has type \lstinline$char * *$, and the result has type \lstinline$char *$. 1072 The expression would be valid if \lstinline$?++$ were declared by 1073 \begin{lstlisting} 1074 forall( otype T ) T * ?++( T * * ); 1075 \end{lstlisting} with \lstinline$T$ inferred to be \lstinline$char$. 1076 1077 \item 1078 ``\lstinline$char *restrict volatile qp; qp++$''. 1079 The result again has type \lstinline$char *$, but the argument now has type \lstinline$char *restrict volatile *$, so it cannot be passed to the hypothetical function declared in point 1. 1080 Hence the actual predefined function is 1081 \begin{lstlisting} 1082 forall( otype T ) T * ?++( T * restrict volatile * ); 1083 \end{lstlisting} which also accepts a \lstinline$char * *$ argument, because of the safe conversions that add 1084 \lstinline$volatile$ and \lstinline$restrict$ qualifiers. (The parameter is not const-qualified, so constant pointers cannot be incremented.) 1085 1086 \item 1087 ``\lstinline$char *_Atomic ap; ap++$''. 1088 The result again has type \lstinline$char *$, but no safe conversion adds an \lstinline$_Atomic$ qualifier, so the function in point 2 is not applicable. 1089 A separate overloading of \lstinline$?++$ is required. 1090 1091 \item 1092 ``\lstinline$char const volatile * pq; pq++$''. 1093 Here the result has type 1415 1094 \lstinline$char const volatile *$, so a new overloading is needed: 1416 1095 \begin{lstlisting} 1417 forall( type T ) T const volatile * ?++( T const volatile *restrict volatile * ); 1418 \end{lstlisting} 1419 One overloading is needed for each combination of qualifiers in the pointed-at 1420 type\index{deficiencies!pointers to qualified types}. 1096 forall( otype T ) T const volatile * ?++( T const volatile *restrict volatile * ); 1097 \end{lstlisting} 1098 One overloading is needed for each combination of qualifiers in the pointed-at type\index{deficiencies!pointers to qualified types}. 1421 1099 1422 1100 \item 1423 ``\lstinline$float *restrict * prp; prp++$''. The \lstinline$restrict$ qualifier is handled just 1424 like \lstinline$const$ and \lstinline$volatile$ in the previous case: 1425 \begin{lstlisting} 1426 forall( type T ) T restrict * ?++( T restrict *restrict volatile * ); 1427 \end{lstlisting} 1428 with \lstinline$T$ inferred to be \lstinline$float *$. This looks odd, because {\c11} contains a 1429 constraint that requires restrict-qualified types to be pointer-to-object types, and \lstinline$T$ 1430 is not syntactically a pointer type. \CFA loosens the constraint. 1101 ``\lstinline$float *restrict * prp; prp++$''. 1102 The \lstinline$restrict$ qualifier is handled just like \lstinline$const$ and \lstinline$volatile$ in the previous case: 1103 \begin{lstlisting} 1104 forall( otype T ) T restrict * ?++( T restrict *restrict volatile * ); 1105 \end{lstlisting} with \lstinline$T$ inferred to be \lstinline$float *$. 1106 This looks odd, because {\c11} contains a constraint that requires restrict-qualified types to be pointer-to-object types, and \lstinline$T$ is not syntactically a pointer type. \CFA loosens the constraint. 1431 1107 \end{enumerate} 1432 1108 \end{rationale} … … 1436 1112 1437 1113 \semantics 1438 A compound literal has one interpretation, with the type given by the \nonterm{type-name} of the 1439 compound literal. 1114 A compound literal has one interpretation, with the type given by the \nonterm{type-name} of the compound literal. 1440 1115 1441 1116 … … 1455 1130 \rewriterules 1456 1131 \begin{lstlisting} 1457 *a @\rewrite@ *?( a) @\use{*?}@1458 +a @\rewrite@ +?( a) @\use{+?}@1459 -a @\rewrite@ -?( a) @\use{-?}@1460 ~a @\rewrite@ ~?( a) @\use{~?}@1461 !a @\rewrite@ !?( a) @\use{"!?}@1462 ++a @\rewrite@ ++?(&( a)) @\use{++?}@1463 --a @\rewrite@ --?(&( a)) @\use{--?}@1132 *a @\rewrite@ *?( a ) @\use{*?}@ 1133 +a @\rewrite@ +?( a ) @\use{+?}@ 1134 -a @\rewrite@ -?( a ) @\use{-?}@ 1135 ~a @\rewrite@ ~?( a ) @\use{~?}@ 1136 !a @\rewrite@ !?( a ) @\use{"!?}@ 1137 ++a @\rewrite@ ++?(&( a )) @\use{++?}@ 1138 --a @\rewrite@ --?(&( a )) @\use{--?}@ 1464 1139 \end{lstlisting} 1465 1140 … … 1469 1144 \predefined 1470 1145 \begin{lstlisting} 1471 _Bool ++?( volatile _Bool * ), 1472 ++?( _Atomic volatile _Bool * ); 1473 char ++?( volatile char * ), 1474 ++?( _Atomic volatile char * ); 1475 signed char ++?( volatile signed char * ), 1476 ++?( _Atomic volatile signed char * ); 1477 unsigned char ++?( volatile signed char * ), 1478 ++?( _Atomic volatile signed char * ); 1479 short int ++?( volatile short int * ), 1480 ++?( _Atomic volatile short int * ); 1481 unsigned short int ++?( volatile unsigned short int * ), 1482 ++?( _Atomic volatile unsigned short int * ); 1483 int ++?( volatile int * ), 1484 ++?( _Atomic volatile int * ); 1485 unsigned int ++?( volatile unsigned int * ), 1486 ++?( _Atomic volatile unsigned int * ); 1487 long int ++?( volatile long int * ), 1488 ++?( _Atomic volatile long int * ); 1489 long unsigned int ++?( volatile long unsigned int * ), 1490 ++?( _Atomic volatile long unsigned int * ); 1491 long long int ++?( volatile long long int * ), 1492 ++?( _Atomic volatile long long int * ); 1493 long long unsigned ++?( volatile long long unsigned int * ), 1494 ++?( _Atomic volatile long long unsigned int * ); 1495 float ++?( volatile float * ), 1496 ++?( _Atomic volatile float * ); 1497 double ++?( volatile double * ), 1498 ++?( _Atomic volatile double * ); 1499 long double ++?( volatile long double * ), 1500 ++?( _Atomic volatile long double * ); 1501 1502 forall( type T ) T * ++?( T * restrict volatile * ), 1503 * ++?( T * _Atomic restrict volatile * ); 1504 1505 forall( type T ) _Atomic T * ++?( _Atomic T * restrict volatile * ), 1506 * ++?( _Atomic T * _Atomic restrict volatile * ); 1507 1508 forall( type T ) const T * ++?( const T * restrict volatile * ), 1509 * ++?( const T * _Atomic restrict volatile * ); 1510 1511 forall( type T ) volatile T * ++?( volatile T * restrict volatile * ), 1512 * ++?( volatile T * _Atomic restrict volatile * ); 1513 1514 forall( type T ) restrict T * ++?( restrict T * restrict volatile * ), 1515 * ++?( restrict T * _Atomic restrict volatile * ); 1516 1517 forall( type T ) _Atomic const T * ++?( _Atomic const T * restrict volatile * ), 1146 _Bool ++?( volatile _Bool * ), ++?( _Atomic volatile _Bool * ); 1147 char ++?( volatile char * ), ++?( _Atomic volatile char * ); 1148 signed char ++?( volatile signed char * ), ++?( _Atomic volatile signed char * ); 1149 unsigned char ++?( volatile signed char * ), ++?( _Atomic volatile signed char * ); 1150 short int ++?( volatile short int * ), ++?( _Atomic volatile short int * ); 1151 unsigned short int ++?( volatile unsigned short int * ), ++?( _Atomic volatile unsigned short int * ); 1152 int ++?( volatile int * ), ++?( _Atomic volatile int * ); 1153 unsigned int ++?( volatile unsigned int * ), ++?( _Atomic volatile unsigned int * ); 1154 long int ++?( volatile long int * ), ++?( _Atomic volatile long int * ); 1155 long unsigned int ++?( volatile long unsigned int * ), ++?( _Atomic volatile long unsigned int * ); 1156 long long int ++?( volatile long long int * ), ++?( _Atomic volatile long long int * ); 1157 long long unsigned ++?( volatile long long unsigned int * ), ++?( _Atomic volatile long long unsigned int * ); 1158 float ++?( volatile float * ), ++?( _Atomic volatile float * ); 1159 double ++?( volatile double * ), ++?( _Atomic volatile double * ); 1160 long double ++?( volatile long double * ), ++?( _Atomic volatile long double * ); 1161 1162 forall( otype T ) T * ++?( T * restrict volatile * ), * ++?( T * _Atomic restrict volatile * ); 1163 forall( otype T ) _Atomic T * ++?( _Atomic T * restrict volatile * ), * ++?( _Atomic T * _Atomic restrict volatile * ); 1164 forall( otype T ) const T * ++?( const T * restrict volatile * ), * ++?( const T * _Atomic restrict volatile * ); 1165 forall( otype T ) volatile T * ++?( volatile T * restrict volatile * ), * ++?( volatile T * _Atomic restrict volatile * ); 1166 forall( otype T ) restrict T * ++?( restrict T * restrict volatile * ), * ++?( restrict T * _Atomic restrict volatile * ); 1167 forall( otype T ) _Atomic const T * ++?( _Atomic const T * restrict volatile * ), 1518 1168 * ++?( _Atomic const T * _Atomic restrict volatile * ); 1519 1520 forall( type T ) _Atomic volatile T * ++?( _Atomic volatile T * restrict volatile * ), 1169 forall( otype T ) _Atomic volatile T * ++?( _Atomic volatile T * restrict volatile * ), 1521 1170 * ++?( _Atomic volatile T * _Atomic restrict volatile * ); 1522 1523 forall( type T ) _Atomic restrict T * ++?( _Atomic restrict T * restrict volatile * ), 1171 forall( otype T ) _Atomic restrict T * ++?( _Atomic restrict T * restrict volatile * ), 1524 1172 * ++?( _Atomic restrict T * _Atomic restrict volatile * ); 1525 1526 forall( type T ) const volatile T * ++?( const volatile T * restrict volatile * ), 1173 forall( otype T ) const volatile T * ++?( const volatile T * restrict volatile * ), 1527 1174 * ++?( const volatile T * _Atomic restrict volatile * ); 1528 1529 forall( type T ) const restrict T * ++?( const restrict T * restrict volatile * ), 1175 forall( otype T ) const restrict T * ++?( const restrict T * restrict volatile * ), 1530 1176 * ++?( const restrict T * _Atomic restrict volatile * ); 1531 1532 forall( type T ) restrict volatile T * ++?( restrict volatile T * restrict volatile * ), 1177 forall( otype T ) restrict volatile T * ++?( restrict volatile T * restrict volatile * ), 1533 1178 * ++?( restrict volatile T * _Atomic restrict volatile * ); 1534 1535 forall( type T ) _Atomic const volatile T * ++?( _Atomic const volatile T * restrict volatile * ), 1179 forall( otype T ) _Atomic const volatile T * ++?( _Atomic const volatile T * restrict volatile * ), 1536 1180 * ++?( _Atomic const volatile T * _Atomic restrict volatile * ); 1537 1538 forall( type T ) _Atomic const restrict T * ++?( _Atomic const restrict T * restrict volatile * ), 1181 forall( otype T ) _Atomic const restrict T * ++?( _Atomic const restrict T * restrict volatile * ), 1539 1182 * ++?( _Atomic const restrict T * _Atomic restrict volatile * ); 1540 1541 forall( type T ) _Atomic restrict volatile T * ++?( _Atomic restrict volatile T * restrict volatile * ), 1183 forall( otype T ) _Atomic restrict volatile T * ++?( _Atomic restrict volatile T * restrict volatile * ), 1542 1184 * ++?( _Atomic restrict volatile T * _Atomic restrict volatile * ); 1543 1544 forall( type T ) const restrict volatile T * ++?( const restrict volatile T * restrict volatile * ), 1185 forall( otype T ) const restrict volatile T * ++?( const restrict volatile T * restrict volatile * ), 1545 1186 * ++?( const restrict volatile T * _Atomic restrict volatile * ); 1546 1547 forall( type T ) _Atomic const restrict volatile T * ++?( _Atomic const restrict volatile T * restrict volatile * ), 1187 forall( otype T ) _Atomic const restrict volatile T * ++?( _Atomic const restrict volatile T * restrict volatile * ), 1548 1188 * ++?( _Atomic const restrict volatile T * _Atomic restrict volatile * ); 1549 1189 1550 _Bool --?( volatile _Bool * ), 1551 --?( _Atomic volatile _Bool * ); 1552 char --?( volatile char * ), 1553 --?( _Atomic volatile char * ); 1554 signed char --?( volatile signed char * ), 1555 --?( _Atomic volatile signed char * ); 1556 unsigned char --?( volatile signed char * ), 1557 --?( _Atomic volatile signed char * ); 1558 short int --?( volatile short int * ), 1559 --?( _Atomic volatile short int * ); 1560 unsigned short int --?( volatile unsigned short int * ), 1561 --?( _Atomic volatile unsigned short int * ); 1562 int --?( volatile int * ), 1563 --?( _Atomic volatile int * ); 1564 unsigned int --?( volatile unsigned int * ), 1565 --?( _Atomic volatile unsigned int * ); 1566 long int --?( volatile long int * ), 1567 --?( _Atomic volatile long int * ); 1568 long unsigned int --?( volatile long unsigned int * ), 1569 --?( _Atomic volatile long unsigned int * ); 1570 long long int --?( volatile long long int * ), 1571 --?( _Atomic volatile long long int * ); 1572 long long unsigned --?( volatile long long unsigned int * ), 1573 --?( _Atomic volatile long long unsigned int * ); 1574 float --?( volatile float * ), 1575 --?( _Atomic volatile float * ); 1576 double --?( volatile double * ), 1577 --?( _Atomic volatile double * ); 1578 long double --?( volatile long double * ), 1579 --?( _Atomic volatile long double * ); 1580 1581 forall( type T ) T * --?( T * restrict volatile * ), 1582 * --?( T * _Atomic restrict volatile * ); 1583 1584 forall( type T ) _Atomic T * --?( _Atomic T * restrict volatile * ), 1585 * --?( _Atomic T * _Atomic restrict volatile * ); 1586 1587 forall( type T ) const T * --?( const T * restrict volatile * ), 1588 * --?( const T * _Atomic restrict volatile * ); 1589 1590 forall( type T ) volatile T * --?( volatile T * restrict volatile * ), 1591 * --?( volatile T * _Atomic restrict volatile * ); 1592 1593 forall( type T ) restrict T * --?( restrict T * restrict volatile * ), 1594 * --?( restrict T * _Atomic restrict volatile * ); 1595 1596 forall( type T ) _Atomic const T * --?( _Atomic const T * restrict volatile * ), 1190 _Bool --?( volatile _Bool * ), --?( _Atomic volatile _Bool * ); 1191 char --?( volatile char * ), --?( _Atomic volatile char * ); 1192 signed char --?( volatile signed char * ), --?( _Atomic volatile signed char * ); 1193 unsigned char --?( volatile signed char * ), --?( _Atomic volatile signed char * ); 1194 short int --?( volatile short int * ), --?( _Atomic volatile short int * ); 1195 unsigned short int --?( volatile unsigned short int * ), --?( _Atomic volatile unsigned short int * ); 1196 int --?( volatile int * ), --?( _Atomic volatile int * ); 1197 unsigned int --?( volatile unsigned int * ), --?( _Atomic volatile unsigned int * ); 1198 long int --?( volatile long int * ), --?( _Atomic volatile long int * ); 1199 long unsigned int --?( volatile long unsigned int * ), --?( _Atomic volatile long unsigned int * ); 1200 long long int --?( volatile long long int * ), --?( _Atomic volatile long long int * ); 1201 long long unsigned --?( volatile long long unsigned int * ), --?( _Atomic volatile long long unsigned int * ); 1202 float --?( volatile float * ), --?( _Atomic volatile float * ); 1203 double --?( volatile double * ), --?( _Atomic volatile double * ); 1204 long double --?( volatile long double * ), --?( _Atomic volatile long double * ); 1205 1206 forall( otype T ) T * --?( T * restrict volatile * ), * --?( T * _Atomic restrict volatile * ); 1207 forall( otype T ) _Atomic T * --?( _Atomic T * restrict volatile * ), * --?( _Atomic T * _Atomic restrict volatile * ); 1208 forall( otype T ) const T * --?( const T * restrict volatile * ), * --?( const T * _Atomic restrict volatile * ); 1209 forall( otype T ) volatile T * --?( volatile T * restrict volatile * ), * --?( volatile T * _Atomic restrict volatile * ); 1210 forall( otype T ) restrict T * --?( restrict T * restrict volatile * ), * --?( restrict T * _Atomic restrict volatile * ); 1211 forall( otype T ) _Atomic const T * --?( _Atomic const T * restrict volatile * ), 1597 1212 * --?( _Atomic const T * _Atomic restrict volatile * ); 1598 1599 forall( type T ) _Atomic volatile T * --?( _Atomic volatile T * restrict volatile * ), 1213 forall( otype T ) _Atomic volatile T * --?( _Atomic volatile T * restrict volatile * ), 1600 1214 * --?( _Atomic volatile T * _Atomic restrict volatile * ); 1601 1602 forall( type T ) _Atomic restrict T * --?( _Atomic restrict T * restrict volatile * ), 1215 forall( otype T ) _Atomic restrict T * --?( _Atomic restrict T * restrict volatile * ), 1603 1216 * --?( _Atomic restrict T * _Atomic restrict volatile * ); 1604 1605 forall( type T ) const volatile T * --?( const volatile T * restrict volatile * ), 1217 forall( otype T ) const volatile T * --?( const volatile T * restrict volatile * ), 1606 1218 * --?( const volatile T * _Atomic restrict volatile * ); 1607 1608 forall( type T ) const restrict T * --?( const restrict T * restrict volatile * ), 1219 forall( otype T ) const restrict T * --?( const restrict T * restrict volatile * ), 1609 1220 * --?( const restrict T * _Atomic restrict volatile * ); 1610 1611 forall( type T ) restrict volatile T * --?( restrict volatile T * restrict volatile * ), 1221 forall( otype T ) restrict volatile T * --?( restrict volatile T * restrict volatile * ), 1612 1222 * --?( restrict volatile T * _Atomic restrict volatile * ); 1613 1614 forall( type T ) _Atomic const volatile T * --?( _Atomic const volatile T * restrict volatile * ), 1223 forall( otype T ) _Atomic const volatile T * --?( _Atomic const volatile T * restrict volatile * ), 1615 1224 * --?( _Atomic const volatile T * _Atomic restrict volatile * ); 1616 1617 forall( type T ) _Atomic const restrict T * --?( _Atomic const restrict T * restrict volatile * ), 1225 forall( otype T ) _Atomic const restrict T * --?( _Atomic const restrict T * restrict volatile * ), 1618 1226 * --?( _Atomic const restrict T * _Atomic restrict volatile * ); 1619 1620 forall( type T ) _Atomic restrict volatile T * --?( _Atomic restrict volatile T * restrict volatile * ), 1227 forall( otype T ) _Atomic restrict volatile T * --?( _Atomic restrict volatile T * restrict volatile * ), 1621 1228 * --?( _Atomic restrict volatile T * _Atomic restrict volatile * ); 1622 1623 forall( type T ) const restrict volatile T * --?( const restrict volatile T * restrict volatile * ), 1229 forall( otype T ) const restrict volatile T * --?( const restrict volatile T * restrict volatile * ), 1624 1230 * --?( const restrict volatile T * _Atomic restrict volatile * ); 1625 1626 forall( type T ) _Atomic const restrict volatile T * --?( _Atomic const restrict volatile T * restrict volatile * ), 1231 forall( otype T ) _Atomic const restrict volatile T * --?( _Atomic const restrict volatile T * restrict volatile * ), 1627 1232 * --?( _Atomic const restrict volatile T * _Atomic restrict volatile * ); 1628 1233 \end{lstlisting} … … 1645 1250 1646 1251 \semantics 1647 The interpretations of prefix increment and decrement expressions are 1648 determined in the same way as the interpretations of postfix increment and 1649 decrement expressions. 1252 The interpretations of prefix increment and decrement expressions are determined in the same way as the interpretations of postfix increment and decrement expressions. 1650 1253 1651 1254 … … 1654 1257 \predefined 1655 1258 \begin{lstlisting} 1656 forall( type T ) lvalue T *?( T * ); 1657 forall( type T ) _Atomic lvalue T *?( _Atomic T * ); 1658 forall( type T ) const lvalue T *?( const T * ); 1659 forall( type T ) volatile lvalue T *?( volatile T * ); 1660 forall( type T ) restrict lvalue T *?( restrict T * ); 1661 forall( type T ) _Atomic const lvalue T *?( _Atomic const T * ); 1662 forall( type T ) _Atomic volatile lvalue T *?( _Atomic volatile T * ); 1663 forall( type T ) _Atomic restrict lvalue T *?( _Atomic restrict T * ); 1664 forall( type T ) const volatile lvalue T *?( const volatile T * ); 1665 forall( type T ) const restrict lvalue T *?( const restrict T * ); 1666 forall( type T ) restrict volatile lvalue T *?( restrict volatile T * ); 1667 forall( type T ) _Atomic const volatile lvalue T *?( _Atomic const volatile T * ); 1668 forall( type T ) _Atomic const restrict lvalue T *?( _Atomic const restrict T * ); 1669 forall( type T ) _Atomic restrict volatile lvalue T *?( _Atomic restrict volatile T * ); 1670 forall( type T ) const restrict volatile lvalue T *?( const restrict volatile T * ); 1671 forall( type T ) _Atomic const restrict volatile lvalue T *?( _Atomic const restrict volatile T * ); 1672 1259 forall( otype T ) lvalue T *?( T * ); 1260 forall( otype T ) _Atomic lvalue T *?( _Atomic T * ); 1261 forall( otype T ) const lvalue T *?( const T * ); 1262 forall( otype T ) volatile lvalue T *?( volatile T * ); 1263 forall( otype T ) restrict lvalue T *?( restrict T * ); 1264 forall( otype T ) _Atomic const lvalue T *?( _Atomic const T * ); 1265 forall( otype T ) _Atomic volatile lvalue T *?( _Atomic volatile T * ); 1266 forall( otype T ) _Atomic restrict lvalue T *?( _Atomic restrict T * ); 1267 forall( otype T ) const volatile lvalue T *?( const volatile T * ); 1268 forall( otype T ) const restrict lvalue T *?( const restrict T * ); 1269 forall( otype T ) restrict volatile lvalue T *?( restrict volatile T * ); 1270 forall( otype T ) _Atomic const volatile lvalue T *?( _Atomic const volatile T * ); 1271 forall( otype T ) _Atomic const restrict lvalue T *?( _Atomic const restrict T * ); 1272 forall( otype T ) _Atomic restrict volatile lvalue T *?( _Atomic restrict volatile T * ); 1273 forall( otype T ) const restrict volatile lvalue T *?( const restrict volatile T * ); 1274 forall( otype T ) _Atomic const restrict volatile lvalue T *?( _Atomic const restrict volatile T * ); 1673 1275 forall( ftype FT ) FT *?( FT * ); 1674 1276 \end{lstlisting} … … 1682 1284 \lstinline$T$ is the type of the operand. 1683 1285 1684 The interpretations of an indirection expression are the interpretations of the corresponding 1685 function call. 1286 The interpretations of an indirection expression are the interpretations of the corresponding function call. 1686 1287 1687 1288 … … 1690 1291 \predefined 1691 1292 \begin{lstlisting} 1692 int 1693 +?( int ), 1694 -?( int ), 1695 ~?( int ); 1696 unsigned int 1697 +?( unsigned int ), 1698 -?( unsigned int ), 1699 ~?( unsigned int ); 1700 long int 1701 +?( long int ), 1702 -?( long int ), 1703 ~?( long int ); 1704 long unsigned int 1705 +?( long unsigned int ), 1706 -?( long unsigned int ), 1707 ~?( long unsigned int ); 1708 long long int 1709 +?( long long int ), 1710 -?( long long int ), 1711 ~?( long long int ); 1712 long long unsigned int 1713 +?( long long unsigned int ), 1714 -?( long long unsigned int ), 1715 ~?( long long unsigned int ); 1716 float 1717 +?( float ), 1718 -?( float ); 1719 double 1720 +?( double ), 1721 -?( double ); 1722 long double 1723 +?( long double ), 1724 -?( long double ); 1725 _Complex float 1726 +?( _Complex float ), 1727 -?( _Complex float ); 1728 _Complex double 1729 +?( _Complex double ), 1730 -?( _Complex double ); 1731 _Complex long double 1732 +?( _Complex long double ), 1733 -?( _Complex long double ); 1734 1735 int !?( int ), 1736 !?( unsigned int ), 1737 !?( long ), 1738 !?( long unsigned int ), 1739 !?( long long int ), 1740 !?( long long unsigned int ), 1741 !?( float ), 1742 !?( double ), 1743 !?( long double ), 1744 !?( _Complex float ), 1745 !?( _Complex double ), 1746 !?( _Complex long double ); 1747 1293 int +?( int ), -?( int ), ~?( int ); 1294 unsigned int +?( unsigned int ), -?( unsigned int ), ~?( unsigned int ); 1295 long int +?( long int ), -?( long int ), ~?( long int ); 1296 long unsigned int +?( long unsigned int ), -?( long unsigned int ), ~?( long unsigned int ); 1297 long long int +?( long long int ), -?( long long int ), ~?( long long int ); 1298 long long unsigned int +?( long long unsigned int ), -?( long long unsigned int ), ~?( long long unsigned int ); 1299 float +?( float ), -?( float ); 1300 double +?( double ), -?( double ); 1301 long double +?( long double ), -?( long double ); 1302 _Complex float +?( _Complex float ), -?( _Complex float ); 1303 _Complex double +?( _Complex double ), -?( _Complex double ); 1304 _Complex long double +?( _Complex long double ), -?( _Complex long double ); 1305 int !?( int ), !?( unsigned int ), !?( long ), !?( long unsigned int ), 1306 !?( long long int ), !?( long long unsigned int ), 1307 !?( float ), !?( double ), !?( long double ), 1308 !?( _Complex float ), !?( _Complex double ), !?( _Complex long double ); 1748 1309 forall( dtype DT ) int !?( const restrict volatile DT * ); 1749 1310 forall( dtype DT ) int !?( _Atomic const restrict volatile DT * ); 1750 1311 forall( ftype FT ) int !?( FT * ); 1751 1312 \end{lstlisting} 1752 For every extended integer type \lstinline$X$ with \Index{integer conversion rank} greater than the 1753 rank of \lstinline$int$ there exist 1313 For every extended integer type \lstinline$X$ with \Index{integer conversion rank} greater than the rank of \lstinline$int$ there exist 1754 1314 % Don't use predefined: keep this out of prelude.cf. 1755 1315 \begin{lstlisting} … … 1759 1319 1760 1320 \semantics 1761 The interpretations of a unary arithmetic expression are the interpretations of the corresponding 1762 function call. 1321 The interpretations of a unary arithmetic expression are the interpretations of the corresponding function call. 1763 1322 1764 1323 \examples … … 1766 1325 long int li; 1767 1326 void eat_double( double );@\use{eat_double}@ 1768 1769 eat_double(-li ); // @\rewrite@ eat_double( -?( li ) ); 1327 eat_double(-li ); // @\rewrite@ eat_double( -?( li ) ); 1770 1328 \end{lstlisting} 1771 1329 The valid interpretations of ``\lstinline$-li$'' (assuming no extended integer types exist) are 1772 1330 \begin{center} 1773 \begin{tabular}{llc} 1774 interpretation & result type & expression conversion cost \\ 1331 \begin{tabular}{llc} interpretation & result type & expression conversion cost \\ 1775 1332 \hline 1776 1333 \lstinline$-?( (int)li )$ & \lstinline$int$ & (unsafe) \\ … … 1788 1345 \end{tabular} 1789 1346 \end{center} 1790 The valid interpretations of the \lstinline$eat_double$ call, with the cost of the argument 1791 conversion and the cost of the entire expression, are 1347 The valid interpretations of the \lstinline$eat_double$ call, with the cost of the argument conversion and the cost of the entire expression, are 1792 1348 \begin{center} 1793 \begin{tabular}{lcc} 1794 interpretation & argument cost & expression cost \\ 1349 \begin{tabular}{lcc} interpretation & argument cost & expression cost \\ 1795 1350 \hline 1796 1351 \lstinline$eat_double( (double)-?( (int)li) )$ & 7 & (unsafe) \\ … … 1808 1363 \end{tabular} 1809 1364 \end{center} 1810 Each has result type \lstinline$void$, so the best must be selected. The interpretations involving 1811 unsafe conversions are discarded. The remainder have equal expression conversion costs, so the 1365 Each has result type \lstinline$void$, so the best must be selected. 1366 The interpretations involving unsafe conversions are discarded. 1367 The remainder have equal expression conversion costs, so the 1812 1368 ``highest argument conversion cost'' rule is invoked, and the chosen interpretation is 1813 1369 \lstinline$eat_double( (double)-?(li) )$. … … 1820 1376 \lstinline$dtype$, or \lstinline$ftype$. 1821 1377 1822 When the \lstinline$sizeof$\use{sizeof} operator is applied to an expression, the expression shall 1823 have exactly one \Index{interpretation}\index{ambiguous interpretation}, which shall 1824 be unambiguous. \semantics A \lstinline$sizeof$ or \lstinline$_Alignof$ expression has one 1825 interpretation, of type \lstinline$size_t$. 1378 When the \lstinline$sizeof$\use{sizeof} operator is applied to an expression, the expression shall have exactly one \Index{interpretation}\index{ambiguous interpretation}, which shall be unambiguous. \semantics A \lstinline$sizeof$ or \lstinline$_Alignof$ expression has one interpretation, of type \lstinline$size_t$. 1826 1379 1827 1380 When \lstinline$sizeof$ is applied to an identifier declared by a \nonterm{type-declaration} or a 1828 \nonterm{type-parameter}, it yields the size in bytes of the type that implements the operand. When 1829 the operand is an opaque type or an inferred type parameter\index{inferred parameter}, the 1830 expression is not a constant expression. 1381 \nonterm{type-parameter}, it yields the size in bytes of the type that implements the operand. 1382 When the operand is an opaque type or an inferred type parameter\index{inferred parameter}, the expression is not a constant expression. 1831 1383 1832 1384 When \lstinline$_Alignof$ is applied to an identifier declared by a \nonterm{type-declaration} or a 1833 \nonterm{type-parameter}, it yields the alignment requirement of the type that implements the 1834 operand. When the operand is an opaque type or an inferred type parameter\index{inferred 1835 parameter}, the expression is not a constant expression. 1836 \begin{rationale} 1837 \begin{lstlisting} 1838 type Pair = struct { int first, second; }; 1385 \nonterm{type-parameter}, it yields the alignment requirement of the type that implements the operand. 1386 When the operand is an opaque type or an inferred type parameter\index{inferred parameter}, the expression is not a constant expression. 1387 \begin{rationale} 1388 \begin{lstlisting} 1389 otype Pair = struct { int first, second; }; 1839 1390 size_t p_size = sizeof(Pair); // constant expression 1840 1841 extern type Rational;@\use{Rational}@ 1391 extern otype Rational;@\use{Rational}@ 1842 1392 size_t c_size = sizeof(Rational); // non-constant expression 1843 1844 1393 forall(type T) T f(T p1, T p2) { 1845 1394 size_t t_size = sizeof(T); // non-constant expression … … 1847 1396 } 1848 1397 \end{lstlisting} 1849 ``\lstinline$sizeof Rational$'', although not statically known, is fixed. Within \lstinline$f()$, 1398 ``\lstinline$sizeof Rational$'', although not statically known, is fixed. 1399 Within \lstinline$f()$, 1850 1400 ``\lstinline$sizeof(T)$'' is fixed for each call of \lstinline$f()$, but may vary from call to call. 1851 1401 \end{rationale} … … 1867 1417 1868 1418 In a \Index{cast expression} ``\lstinline$($\nonterm{type-name}\lstinline$)e$'', if 1869 \nonterm{type-name} is the type of an interpretation of \lstinline$e$, then that interpretation is 1870 the only interpretation of the cast expression; otherwise, \lstinline$e$ shall have some 1871 interpretation that can be converted to \nonterm{type-name}, and the interpretation of the cast 1872 expression is the cast of the interpretation that can be converted at the lowest cost. The cast 1873 expression's interpretation is ambiguous\index{ambiguous interpretation} if more than one 1874 interpretation can be converted at the lowest cost or if the selected interpretation is ambiguous. 1875 1876 \begin{rationale} 1877 Casts can be used to eliminate ambiguity in expressions by selecting interpretations of 1878 subexpressions, and to specialize polymorphic functions and values. 1419 \nonterm{type-name} is the type of an interpretation of \lstinline$e$, then that interpretation is the only interpretation of the cast expression; 1420 otherwise, \lstinline$e$ shall have some interpretation that can be converted to \nonterm{type-name}, and the interpretation of the cast expression is the cast of the interpretation that can be converted at the lowest cost. 1421 The cast expression's interpretation is ambiguous\index{ambiguous interpretation} if more than one interpretation can be converted at the lowest cost or if the selected interpretation is ambiguous. 1422 1423 \begin{rationale} 1424 Casts can be used to eliminate ambiguity in expressions by selecting interpretations of subexpressions, and to specialize polymorphic functions and values. 1879 1425 \end{rationale} 1880 1426 … … 1899 1445 \predefined 1900 1446 \begin{lstlisting} 1901 int?*?( int, int ), 1902 ?/?( int, int ), 1903 ?%?( int, int ); 1904 unsigned int?*?( unsigned int, unsigned int ), 1905 ?/?( unsigned int, unsigned int ), 1906 ?%?( unsigned int, unsigned int ); 1907 long int?*?( long int, long int ), 1908 ?/?( long, long ), 1909 ?%?( long, long ); 1447 int?*?( int, int ), ?/?( int, int ), ?%?( int, int ); 1448 unsigned int?*?( unsigned int, unsigned int ), ?/?( unsigned int, unsigned int ), ?%?( unsigned int, unsigned int ); 1449 long int?*?( long int, long int ), ?/?( long, long ), ?%?( long, long ); 1910 1450 long unsigned int?*?( long unsigned int, long unsigned int ), 1911 ?/?( long unsigned int, long unsigned int ), 1912 ?%?( long unsigned int, long unsigned int ); 1913 long long int?*?( long long int, long long int ), 1914 ?/?( long long int, long long int ), 1451 ?/?( long unsigned int, long unsigned int ), ?%?( long unsigned int, long unsigned int ); 1452 long long int?*?( long long int, long long int ), ?/?( long long int, long long int ), 1915 1453 ?%?( long long int, long long int ); 1916 1454 long long unsigned int ?*?( long long unsigned int, long long unsigned int ), 1917 ?/?( long long unsigned int, long long unsigned int ), 1918 ?%?( long long unsigned int, long long unsigned int ); 1919 float?*?( float, float ), 1920 ?/?( float, float ); 1921 double?*?( double, double ), 1922 ?/?( double, double ); 1923 long double?*?( long double, long double ), 1924 ?/?( long double, long double ); 1925 _Complex float?*?( float, _Complex float ), 1926 ?/?( float, _Complex float ), 1927 ?*?( _Complex float, float ), 1928 ?/?( _Complex float, float ), 1929 ?*?( _Complex float, _Complex float ), 1930 ?/?( _Complex float, _Complex float ); 1931 _Complex double?*?( double, _Complex double ), 1932 ?/?( double, _Complex double ), 1933 ?*?( _Complex double, double ), 1934 ?/?( _Complex double, double ), 1935 ?*?( _Complex double, _Complex double ), 1936 ?/?( _Complex double, _Complex double ); 1937 _Complex long double?*?( long double, _Complex long double ), 1938 ?/?( long double, _Complex long double ), 1939 ?*?( _Complex long double, long double ), 1940 ?/?( _Complex long double, long double ), 1941 ?*?( _Complex long double, _Complex long double ), 1942 ?/?( _Complex long double, _Complex long double ); 1943 \end{lstlisting} 1944 For every extended integer type \lstinline$X$ with \Index{integer conversion rank} greater than the 1945 rank of \lstinline$int$ there exist 1455 ?/?( long long unsigned int, long long unsigned int ), ?%?( long long unsigned int, long long unsigned int ); 1456 float?*?( float, float ), ?/?( float, float ); 1457 double?*?( double, double ), ?/?( double, double ); 1458 long double?*?( long double, long double ), ?/?( long double, long double ); 1459 _Complex float?*?( float, _Complex float ), ?/?( float, _Complex float ), 1460 ?*?( _Complex float, float ), ?/?( _Complex float, float ), 1461 ?*?( _Complex float, _Complex float ), ?/?( _Complex float, _Complex float ); 1462 _Complex double?*?( double, _Complex double ), ?/?( double, _Complex double ), 1463 ?*?( _Complex double, double ), ?/?( _Complex double, double ), 1464 ?*?( _Complex double, _Complex double ), ?/?( _Complex double, _Complex double ); 1465 _Complex long double?*?( long double, _Complex long double ), ?/?( long double, _Complex long double ), 1466 ?*?( _Complex long double, long double ), ?/?( _Complex long double, long double ), 1467 ?*?( _Complex long double, _Complex long double ), ?/?( _Complex long double, _Complex long double ); 1468 \end{lstlisting} 1469 For every extended integer type \lstinline$X$ with \Index{integer conversion rank} greater than the rank of \lstinline$int$ there exist 1946 1470 % Don't use predefined: keep this out of prelude.cf. 1947 1471 \begin{lstlisting} … … 1951 1475 \begin{rationale} 1952 1476 {\c11} does not include conversions from the \Index{real type}s to \Index{complex type}s in the 1953 \Index{usual arithmetic conversion}s. Instead it specifies conversion of the result of binary 1954 operations on arguments from mixed type domains. \CFA's predefined operators match that pattern. 1477 \Index{usual arithmetic conversion}s. Instead it specifies conversion of the result of binary operations on arguments from mixed type domains. \CFA's predefined operators match that pattern. 1955 1478 \end{rationale} 1956 1479 1957 1480 \semantics 1958 The interpretations of multiplicative expressions are the interpretations of the corresponding 1959 function call. 1481 The interpretations of multiplicative expressions are the interpretations of the corresponding function call. 1960 1482 1961 1483 \examples … … 1966 1488 eat_double( li % i ); 1967 1489 \end{lstlisting} 1968 ``\lstinline$li % i$'' is rewritten as ``\lstinline$?%?(li, i )$''. The valid interpretations 1969 of \lstinline$?%?(li, i )$, the cost\index{conversion cost} of converting their arguments, and 1970 the cost of converting the result to \lstinline$double$ (assuming no extended integer types are 1971 present ) are 1490 ``\lstinline$li % i$'' is rewritten as ``\lstinline$?%?(li, i )$''. 1491 The valid interpretations of \lstinline$?%?(li, i )$, the cost\index{conversion cost} of converting their arguments, and the cost of converting the result to \lstinline$double$ (assuming no extended integer types are present ) are 1972 1492 \begin{center} 1973 \begin{tabular}{lcc} 1974 interpretation & argument cost & result cost \\ 1493 \begin{tabular}{lcc} interpretation & argument cost & result cost \\ 1975 1494 \hline 1976 1495 \lstinline$ ?%?( (int)li, i )$ & (unsafe) & 6 \\ 1977 1496 \lstinline$ ?%?( (unsigned)li,(unsigned)i )$ & (unsafe) & 5 \\ 1978 \lstinline$ ?%?( li,(long)i )$ & 1 & 4 \\1497 \lstinline$ ?%?( li, (long)i )$ & 1 & 4 \\ 1979 1498 \lstinline$ ?%?( (long unsigned)li,(long unsigned)i )$ & 3 & 3 \\ 1980 1499 \lstinline$ ?%?( (long long)li,(long long)i )$ & 5 & 2 \\ … … 1983 1502 \end{center} 1984 1503 The best interpretation of \lstinline$eat_double( li, i )$ is 1985 \lstinline$eat_double( (double)?%?(li, (long)i ))$, which has no unsafe conversions and the 1986 lowest total cost. 1987 1988 \begin{rationale} 1989 {\c11} defines most arithmetic operations to apply an \Index{integer promotion} to any argument that 1990 belongs to a type that has an \Index{integer conversion rank} less than that of \lstinline$int$.If 1504 \lstinline$eat_double( (double)?%?(li, (long)i ))$, which has no unsafe conversions and the lowest total cost. 1505 1506 \begin{rationale} 1507 {\c11} defines most arithmetic operations to apply an \Index{integer promotion} to any argument that belongs to a type that has an \Index{integer conversion rank} less than that of \lstinline$int$.If 1991 1508 \lstinline$s$ is a \lstinline$short int$, ``\lstinline$s *s$'' does not have type \lstinline$short int$; 1992 it is treated as ``\lstinline$( (int)s ) * ( (int)s )$'', and has type \lstinline$int$. \CFA matches 1993 that pattern; it does not predefine ``\lstinline$short ?*?( short, short )$''. 1994 1995 These ``missing'' operators limit polymorphism. Consider 1996 \begin{lstlisting} 1997 forall( type T | T ?*?( T, T ) ) T square( T ); 1509 it is treated as ``\lstinline$( (int)s ) * ( (int)s )$'', and has type \lstinline$int$. \CFA matches that pattern; 1510 it does not predefine ``\lstinline$short ?*?( short, short )$''. 1511 1512 These ``missing'' operators limit polymorphism. 1513 Consider 1514 \begin{lstlisting} 1515 forall( otype T | T ?*?( T, T ) ) T square( T ); 1998 1516 short s; 1999 1517 square( s ); … … 2001 1519 Since \CFA does not define a multiplication operator for \lstinline$short int$, 2002 1520 \lstinline$square( s )$ is treated as \lstinline$square( (int)s )$, and the result has type 2003 \lstinline$int$. This is mildly surprising, but it follows the {\c11} operator pattern. 1521 \lstinline$int$. 1522 This is mildly surprising, but it follows the {\c11} operator pattern. 2004 1523 2005 1524 A more troubling example is 2006 1525 \begin{lstlisting} 2007 forall( type T | ?*?( T, T ) ) T product( T[], int n );1526 forall( otype T | ?*?( T, T ) ) T product( T[], int n ); 2008 1527 short sa[5]; 2009 1528 product( sa, 5); 2010 1529 \end{lstlisting} 2011 1530 This has no valid interpretations, because \CFA has no conversion from ``array of 2012 \lstinline$short int$'' to ``array of \lstinline$int$''. The alternatives in such situations2013 include1531 \lstinline$short int$'' to ``array of \lstinline$int$''. 1532 The alternatives in such situations include 2014 1533 \begin{itemize} 2015 1534 \item … … 2020 1539 \lstinline$product$. 2021 1540 \item 2022 Defining \lstinline$product$ to take as an argument a conversion function from the ``small'' type to 2023 the operator's argument type. 1541 Defining \lstinline$product$ to take as an argument a conversion function from the ``small'' type to the operator's argument type. 2024 1542 \end{itemize} 2025 1543 \end{rationale} … … 2043 1561 \predefined 2044 1562 \begin{lstlisting} 2045 int?+?( int, int ), 2046 ?-?( int, int ); 2047 unsigned int?+?( unsigned int, unsigned int ), 2048 ?-?( unsigned int, unsigned int ); 2049 long int?+?( long int, long int ), 2050 ?-?( long int, long int ); 2051 long unsigned int?+?( long unsigned int, long unsigned int ), 2052 ?-?( long unsigned int, long unsigned int ); 2053 long long int?+?( long long int, long long int ), 2054 ?-?( long long int, long long int ); 1563 int?+?( int, int ), ?-?( int, int ); 1564 unsigned int?+?( unsigned int, unsigned int ), ?-?( unsigned int, unsigned int ); 1565 long int?+?( long int, long int ), ?-?( long int, long int ); 1566 long unsigned int?+?( long unsigned int, long unsigned int ), ?-?( long unsigned int, long unsigned int ); 1567 long long int?+?( long long int, long long int ), ?-?( long long int, long long int ); 2055 1568 long long unsigned int ?+?( long long unsigned int, long long unsigned int ), 2056 1569 ?-?( long long unsigned int, long long unsigned int ); 2057 float?+?( float, float ), 2058 ?-?( float, float ); 2059 double?+?( double, double ), 2060 ?-?( double, double ); 2061 long double?+?( long double, long double ), 2062 ?-?( long double, long double ); 2063 _Complex float?+?( _Complex float, float ), 2064 ?-?( _Complex float, float ), 2065 ?+?( float, _Complex float ), 2066 ?-?( float, _Complex float ), 2067 ?+?( _Complex float, _Complex float ), 2068 ?-?( _Complex float, _Complex float ); 2069 _Complex double?+?( _Complex double, double ), 2070 ?-?( _Complex double, double ), 2071 ?+?( double, _Complex double ), 2072 ?-?( double, _Complex double ), 2073 ?+?( _Complex double, _Complex double ), 2074 ?-?( _Complex double, _Complex double ); 2075 _Complex long double?+?( _Complex long double, long double ), 2076 ?-?( _Complex long double, long double ), 2077 ?+?( long double, _Complex long double ), 2078 ?-?( long double, _Complex long double ), 2079 ?+?( _Complex long double, _Complex long double ), 2080 ?-?( _Complex long double, _Complex long double ); 2081 2082 forall( type T ) T 2083 * ?+?( T *, ptrdiff_t ), 2084 * ?+?( ptrdiff_t, T * ), 2085 * ?-?( T *, ptrdiff_t ); 2086 2087 forall( type T ) _Atomic T 2088 * ?+?( _Atomic T *, ptrdiff_t ), 2089 * ?+?( ptrdiff_t, _Atomic T * ), 1570 float?+?( float, float ), ?-?( float, float ); 1571 double?+?( double, double ), ?-?( double, double ); 1572 long double?+?( long double, long double ), ?-?( long double, long double ); 1573 _Complex float?+?( _Complex float, float ), ?-?( _Complex float, float ), 1574 ?+?( float, _Complex float ), ?-?( float, _Complex float ), 1575 ?+?( _Complex float, _Complex float ), ?-?( _Complex float, _Complex float ); 1576 _Complex double?+?( _Complex double, double ), ?-?( _Complex double, double ), 1577 ?+?( double, _Complex double ), ?-?( double, _Complex double ), 1578 ?+?( _Complex double, _Complex double ), ?-?( _Complex double, _Complex double ); 1579 _Complex long double?+?( _Complex long double, long double ), ?-?( _Complex long double, long double ), 1580 ?+?( long double, _Complex long double ), ?-?( long double, _Complex long double ), 1581 ?+?( _Complex long double, _Complex long double ), ?-?( _Complex long double, _Complex long double ); 1582 1583 forall( otype T ) T * ?+?( T *, ptrdiff_t ), * ?+?( ptrdiff_t, T * ), * ?-?( T *, ptrdiff_t ); 1584 forall( otype T ) _Atomic T * ?+?( _Atomic T *, ptrdiff_t ), * ?+?( ptrdiff_t, _Atomic T * ), 2090 1585 * ?-?( _Atomic T *, ptrdiff_t ); 2091 2092 forall( type T ) const T 2093 * ?+?( const T *, ptrdiff_t ), 2094 * ?+?( ptrdiff_t, const T * ), 1586 forall( otype T ) const T * ?+?( const T *, ptrdiff_t ), * ?+?( ptrdiff_t, const T * ), 2095 1587 * ?-?( const T *, ptrdiff_t ); 2096 2097 forall( type T ) restrict T 2098 * ?+?( restrict T *, ptrdiff_t ), 2099 * ?+?( ptrdiff_t, restrict T * ), 1588 forall( otype T ) restrict T * ?+?( restrict T *, ptrdiff_t ), * ?+?( ptrdiff_t, restrict T * ), 2100 1589 * ?-?( restrict T *, ptrdiff_t ); 2101 2102 forall( type T ) volatile T 2103 * ?+?( volatile T *, ptrdiff_t ), 2104 * ?+?( ptrdiff_t, volatile T * ), 1590 forall( otype T ) volatile T * ?+?( volatile T *, ptrdiff_t ), * ?+?( ptrdiff_t, volatile T * ), 2105 1591 * ?-?( volatile T *, ptrdiff_t ); 2106 2107 forall( type T ) _Atomic const T 2108 * ?+?( _Atomic const T *, ptrdiff_t ), 2109 * ?+?( ptrdiff_t, _Atomic const T * ), 1592 forall( otype T ) _Atomic const T * ?+?( _Atomic const T *, ptrdiff_t ), * ?+?( ptrdiff_t, _Atomic const T * ), 2110 1593 * ?-?( _Atomic const T *, ptrdiff_t ); 2111 2112 forall( type T ) _Atomic restrict T 2113 * ?+?( _Atomic restrict T *, ptrdiff_t ), 2114 * ?+?( ptrdiff_t, _Atomic restrict T * ), 1594 forall( otype T ) _Atomic restrict T * ?+?( _Atomic restrict T *, ptrdiff_t ), * ?+?( ptrdiff_t, _Atomic restrict T * ), 2115 1595 * ?-?( _Atomic restrict T *, ptrdiff_t ); 2116 2117 forall( type T ) _Atomic volatile T 2118 * ?+?( _Atomic volatile T *, ptrdiff_t ), 2119 * ?+?( ptrdiff_t, _Atomic volatile T * ), 1596 forall( otype T ) _Atomic volatile T * ?+?( _Atomic volatile T *, ptrdiff_t ), * ?+?( ptrdiff_t, _Atomic volatile T * ), 2120 1597 * ?-?( _Atomic volatile T *, ptrdiff_t ); 2121 2122 forall( type T ) const restrict T 2123 * ?+?( const restrict T *, ptrdiff_t ), 2124 * ?+?( ptrdiff_t, const restrict T * ), 1598 forall( otype T ) const restrict T * ?+?( const restrict T *, ptrdiff_t ), * ?+?( ptrdiff_t, const restrict T * ), 2125 1599 * ?-?( const restrict T *, ptrdiff_t ); 2126 2127 forall( type T ) const volatile T 2128 * ?+?( const volatile T *, ptrdiff_t ), 2129 * ?+?( ptrdiff_t, const volatile T * ), 1600 forall( otype T ) const volatile T * ?+?( const volatile T *, ptrdiff_t ), * ?+?( ptrdiff_t, const volatile T * ), 2130 1601 * ?-?( const volatile T *, ptrdiff_t ); 2131 2132 forall( type T ) restrict volatile T 2133 * ?+?( restrict volatile T *, ptrdiff_t ), 2134 * ?+?( ptrdiff_t, restrict volatile T * ), 1602 forall( otype T ) restrict volatile T * ?+?( restrict volatile T *, ptrdiff_t ), * ?+?( ptrdiff_t, restrict volatile T * ), 2135 1603 * ?-?( restrict volatile T *, ptrdiff_t ); 2136 2137 forall( type T ) _Atomic const restrict T 2138 * ?+?( _Atomic const restrict T *, ptrdiff_t ), 1604 forall( otype T ) _Atomic const restrict T * ?+?( _Atomic const restrict T *, ptrdiff_t ), 2139 1605 * ?+?( ptrdiff_t, _Atomic const restrict T * ), 2140 1606 * ?-?( _Atomic const restrict T *, ptrdiff_t ); 2141 2142 forall( type T ) ptrdiff_t 1607 forall( otype T ) ptrdiff_t 2143 1608 * ?-?( const restrict volatile T *, const restrict volatile T * ), 2144 1609 * ?-?( _Atomic const restrict volatile T *, _Atomic const restrict volatile T * ); 2145 1610 \end{lstlisting} 2146 For every extended integer type \lstinline$X$ with \Index{integer conversion rank} greater than the 2147 rank of \lstinline$int$ there exist 1611 For every extended integer type \lstinline$X$ with \Index{integer conversion rank} greater than the rank of \lstinline$int$ there exist 2148 1612 % Don't use predefined: keep this out of prelude.cf. 2149 1613 \begin{lstlisting} … … 2152 1616 2153 1617 \semantics 2154 The interpretations of additive expressions are the interpretations of the corresponding function 2155 calls. 2156 2157 \begin{rationale} 2158 \lstinline$ptrdiff_t$ is an implementation-defined identifier defined in \lstinline$<stddef.h>$ that 2159 is synonymous with a signed integral type that is large enough to hold the difference between two 2160 pointers. It seems reasonable to use it for pointer addition as well. (This is technically a 2161 difference between \CFA and C, which only specifies that pointer addition uses an \emph{integral} 2162 argument.) Hence it is also used for subscripting, which is defined in terms of pointer addition. 2163 The {\c11} standard uses \lstinline$size_t$ in several cases where a library function takes an 2164 argument that is used as a subscript, but \lstinline$size_t$ is unsuitable here because it is an 2165 unsigned type. 1618 The interpretations of additive expressions are the interpretations of the corresponding function calls. 1619 1620 \begin{rationale} 1621 \lstinline$ptrdiff_t$ is an implementation-defined identifier defined in \lstinline$<stddef.h>$ that is synonymous with a signed integral type that is large enough to hold the difference between two pointers. 1622 It seems reasonable to use it for pointer addition as well. (This is technically a difference between \CFA and C, which only specifies that pointer addition uses an \emph{integral} argument.) Hence it is also used for subscripting, which is defined in terms of pointer addition. 1623 The {\c11} standard uses \lstinline$size_t$ in several cases where a library function takes an argument that is used as a subscript, but \lstinline$size_t$ is unsuitable here because it is an unsigned type. 2166 1624 \end{rationale} 2167 1625 … … 2184 1642 \predefined 2185 1643 \begin{lstlisting} 2186 int ?<<?( int, int ), 2187 ?>>?( int, int ); 2188 unsigned int ?<<?( unsigned int, int ), 2189 ?>>?( unsigned int, int ); 2190 long int ?<<?( long int, int ), 2191 ?>>?( long int, int ); 2192 long unsigned int ?<<?( long unsigned int, int ), 2193 ?>>?( long unsigned int, int ); 2194 long long int ?<<?( long long int, int ), 2195 ?>>?( long long int, int ); 2196 long long unsigned int ?<<?( long long unsigned int, int ), 2197 ?>>?( long long unsigned int, int); 2198 \end{lstlisting} 2199 For every extended integer type \lstinline$X$ with \Index{integer conversion rank} greater than the 2200 rank of \lstinline$int$ there exist 1644 int ?<<?( int, int ), ?>>?( int, int ); 1645 unsigned int ?<<?( unsigned int, int ), ?>>?( unsigned int, int ); 1646 long int ?<<?( long int, int ), ?>>?( long int, int ); 1647 long unsigned int ?<<?( long unsigned int, int ), ?>>?( long unsigned int, int ); 1648 long long int ?<<?( long long int, int ), ?>>?( long long int, int ); 1649 long long unsigned int ?<<?( long long unsigned int, int ), ?>>?( long long unsigned int, int); 1650 \end{lstlisting} 1651 For every extended integer type \lstinline$X$ with \Index{integer conversion rank} greater than the rank of \lstinline$int$ there exist 2201 1652 % Don't use predefined: keep this out of prelude.cf. 2202 1653 \begin{lstlisting} … … 2205 1656 2206 1657 \begin{rationale} 2207 The bitwise shift operators break the usual pattern: they do not convert both operands to a common 2208 type.The right operand only undergoes \Index{integer promotion}.1658 The bitwise shift operators break the usual pattern: they do not convert both operands to a common type. 1659 The right operand only undergoes \Index{integer promotion}. 2209 1660 \end{rationale} 2210 1661 2211 1662 \semantics 2212 The interpretations of a bitwise shift expression are the interpretations of the corresponding 2213 function calls. 1663 The interpretations of a bitwise shift expression are the interpretations of the corresponding function calls. 2214 1664 2215 1665 … … 2235 1685 \predefined 2236 1686 \begin{lstlisting} 2237 int ?<?( int, int ), 2238 ?<=?( int, int ), 2239 ?>?( int, int ), 2240 ?>=?( int, int ); 2241 int ?<?( unsigned int, unsigned int ), 2242 ?<=?( unsigned int, unsigned int ), 2243 ?>?( unsigned int, unsigned int ), 2244 ?>=?( unsigned int, unsigned int ); 2245 int ?<?( long int, long int ), 2246 ?<=?( long int, long int ), 2247 ?>?( long int, long int ), 2248 ?>=?( long int, long int ); 2249 int ?<?( long unsigned int, long unsigned ), 2250 ?<=?( long unsigned int, long unsigned ), 2251 ?>?( long unsigned int, long unsigned ), 2252 ?>=?( long unsigned int, long unsigned ); 2253 int ?<?( long long int, long long int ), 2254 ?<=?( long long int, long long int ), 2255 ?>?( long long int, long long int ), 2256 ?>=?( long long int, long long int ); 2257 int ?<?( long long unsigned int, long long unsigned ), 2258 ?<=?( long long unsigned int, long long unsigned ), 2259 ?>?( long long unsigned int, long long unsigned ), 2260 ?>=?( long long unsigned int, long long unsigned ); 2261 int ?<?( float, float ), 2262 ?<=?( float, float ), 2263 ?>?( float, float ), 2264 ?>=?( float, float ); 2265 int ?<?( double, double ), 2266 ?<=?( double, double ), 2267 ?>?( double, double ), 2268 ?>=?( double, double ); 2269 int ?<?( long double, long double ), 2270 ?<=?( long double, long double ), 2271 ?>?( long double, long double ), 2272 ?>=?( long double, long double ); 2273 2274 forall( dtype DT ) int 2275 ?<?( const restrict volatile DT *, const restrict volatile DT * ), 1687 int ?<?( int, int ), ?<=?( int, int ), 1688 ?>?( int, int ), ?>=?( int, int ); 1689 int ?<?( unsigned int, unsigned int ), ?<=?( unsigned int, unsigned int ), 1690 ?>?( unsigned int, unsigned int ), ?>=?( unsigned int, unsigned int ); 1691 int ?<?( long int, long int ), ?<=?( long int, long int ), 1692 ?>?( long int, long int ), ?>=?( long int, long int ); 1693 int ?<?( long unsigned int, long unsigned ), ?<=?( long unsigned int, long unsigned ), 1694 ?>?( long unsigned int, long unsigned ), ?>=?( long unsigned int, long unsigned ); 1695 int ?<?( long long int, long long int ), ?<=?( long long int, long long int ), 1696 ?>?( long long int, long long int ), ?>=?( long long int, long long int ); 1697 int ?<?( long long unsigned int, long long unsigned ), ?<=?( long long unsigned int, long long unsigned ), 1698 ?>?( long long unsigned int, long long unsigned ), ?>=?( long long unsigned int, long long unsigned ); 1699 int ?<?( float, float ), ?<=?( float, float ), 1700 ?>?( float, float ), ?>=?( float, float ); 1701 int ?<?( double, double ), ?<=?( double, double ), 1702 ?>?( double, double ), ?>=?( double, double ); 1703 int ?<?( long double, long double ), ?<=?( long double, long double ), 1704 ?>?( long double, long double ), ?>=?( long double, long double ); 1705 forall( dtype DT ) int ?<?( const restrict volatile DT *, const restrict volatile DT * ), 2276 1706 ?<?( _Atomic const restrict volatile DT *, _Atomic const restrict volatile DT * ), 2277 1707 ?<=?( const restrict volatile DT *, const restrict volatile DT * ), … … 2282 1712 ?>=?( _Atomic const restrict volatile DT *, _Atomic const restrict volatile DT * ); 2283 1713 \end{lstlisting} 2284 For every extended integer type \lstinline$X$ with \Index{integer conversion rank} greater than the 2285 rank of \lstinline$int$ there exist 1714 For every extended integer type \lstinline$X$ with \Index{integer conversion rank} greater than the rank of \lstinline$int$ there exist 2286 1715 % Don't use predefined: keep this out of prelude.cf. 2287 1716 \begin{lstlisting} … … 2293 1722 2294 1723 \semantics 2295 The interpretations of a relational expression are the interpretations of the corresponding function 2296 call. 1724 The interpretations of a relational expression are the interpretations of the corresponding function call. 2297 1725 2298 1726 … … 2314 1742 \predefined 2315 1743 \begin{lstlisting} 2316 int ?==?( int, int ), 2317 ?!=?( int, int ), 2318 ?==?( unsigned int, unsigned int ), 2319 ?!=?( unsigned int, unsigned int ), 2320 ?==?( long int, long int ), 2321 ?!=?( long int, long int ), 2322 ?==?( long unsigned int, long unsigned int ), 2323 ?!=?( long unsigned int, long unsigned int ), 2324 ?==?( long long int, long long int ), 2325 ?!=?( long long int, long long int ), 2326 ?==?( long long unsigned int, long long unsigned int ), 2327 ?!=?( long long unsigned int, long long unsigned int ), 2328 ?==?( float, float ), 2329 ?!=?( float, float ), 2330 ?==?( _Complex float, float ), 2331 ?!=?( _Complex float, float ), 2332 ?==?( float, _Complex float ), 2333 ?!=?( float, _Complex float ), 2334 ?==?( _Complex float, _Complex float ), 2335 ?!=?( _Complex float, _Complex float ), 2336 ?==?( double, double ), 2337 ?!=?( double, double ), 2338 ?==?( _Complex double, double ), 2339 ?!=?( _Complex double, double ), 2340 ?==?( double, _Complex double ), 2341 ?!=?( double, _Complex double ), 2342 ?==?( _Complex double, _Complex double ), 2343 ?!=?( _Complex double, _Complex double ), 2344 ?==?( long double, long double ), 2345 ?!=?( long double, long double ), 2346 ?==?( _Complex long double, long double ), 2347 ?!=?( _Complex long double, long double ), 2348 ?==?( long double, _Complex long double ), 2349 ?!=?( long double, _Complex long double ), 2350 ?==?( _Complex long double, _Complex long double ), 2351 ?!=?( _Complex long double, _Complex long double ); 2352 1744 int ?==?( int, int ), ?!=?( int, int ), 1745 ?==?( unsigned int, unsigned int ), ?!=?( unsigned int, unsigned int ), 1746 ?==?( long int, long int ), ?!=?( long int, long int ), 1747 ?==?( long unsigned int, long unsigned int ), ?!=?( long unsigned int, long unsigned int ), 1748 ?==?( long long int, long long int ), ?!=?( long long int, long long int ), 1749 ?==?( long long unsigned int, long long unsigned int ), ?!=?( long long unsigned int, long long unsigned int ), 1750 ?==?( float, float ), ?!=?( float, float ), 1751 ?==?( _Complex float, float ), ?!=?( _Complex float, float ), 1752 ?==?( float, _Complex float ), ?!=?( float, _Complex float ), 1753 ?==?( _Complex float, _Complex float ), ?!=?( _Complex float, _Complex float ), 1754 ?==?( double, double ), ?!=?( double, double ), 1755 ?==?( _Complex double, double ), ?!=?( _Complex double, double ), 1756 ?==?( double, _Complex double ), ?!=?( double, _Complex double ), 1757 ?==?( _Complex double, _Complex double ), ?!=?( _Complex double, _Complex double ), 1758 ?==?( long double, long double ), ?!=?( long double, long double ), 1759 ?==?( _Complex long double, long double ), ?!=?( _Complex long double, long double ), 1760 ?==?( long double, _Complex long double ), ?!=?( long double, _Complex long double ), 1761 ?==?( _Complex long double, _Complex long double ), ?!=?( _Complex long double, _Complex long double ); 2353 1762 forall( dtype DT ) int 2354 1763 ?==?( const restrict volatile DT *, const restrict volatile DT * ), … … 2375 1784 ?==?( forall( dtype DT2) const DT2*, _Atomic const restrict volatile DT * ), 2376 1785 ?!=?( forall( dtype DT2) const DT2*, _Atomic const restrict volatile DT * ); 2377 2378 1786 forall( ftype FT ) int 2379 ?==?( FT *, FT * ), 2380 ?!=?( FT *, FT * ), 2381 ?==?( FT *, forall( ftype FT2) FT2 * ), 2382 ?!=?( FT *, forall( ftype FT2) FT2 * ), 2383 ?==?( forall( ftype FT2) FT2*, FT * ), 2384 ?!=?( forall( ftype FT2) FT2*, FT * ), 2385 ?==?( forall( ftype FT2) FT2*, forall( ftype FT3) FT3 * ), 2386 ?!=?( forall( ftype FT2) FT2*, forall( ftype FT3) FT3 * ); 2387 \end{lstlisting} 2388 For every extended integer type \lstinline$X$ with \Index{integer conversion rank} greater than the 2389 rank of \lstinline$int$ there exist 1787 ?==?( FT *, FT * ), ?!=?( FT *, FT * ), 1788 ?==?( FT *, forall( ftype FT2) FT2 * ), ?!=?( FT *, forall( ftype FT2) FT2 * ), 1789 ?==?( forall( ftype FT2) FT2*, FT * ), ?!=?( forall( ftype FT2) FT2*, FT * ), 1790 ?==?( forall( ftype FT2) FT2*, forall( ftype FT3) FT3 * ), ?!=?( forall( ftype FT2) FT2*, forall( ftype FT3) FT3 * ); 1791 \end{lstlisting} 1792 For every extended integer type \lstinline$X$ with \Index{integer conversion rank} greater than the rank of \lstinline$int$ there exist 2390 1793 % Don't use predefined: keep this out of prelude.cf. 2391 1794 \begin{lstlisting} … … 2395 1798 2396 1799 \begin{rationale} 2397 The polymorphic equality operations come in three styles: comparisons between pointers of compatible 2398 types, between pointers to \lstinline$void$ and pointers to object types or incomplete types, and 2399 between the \Index{null pointer} constant and pointers to any type. In the last case, a special 2400 constraint rule for null pointer constant operands has been replaced by a consequence of the \CFA 2401 type system. 1800 The polymorphic equality operations come in three styles: comparisons between pointers of compatible types, between pointers to \lstinline$void$ and pointers to object types or incomplete types, and between the \Index{null pointer} constant and pointers to any type. 1801 In the last case, a special constraint rule for null pointer constant operands has been replaced by a consequence of the \CFA type system. 2402 1802 \end{rationale} 2403 1803 2404 1804 \semantics 2405 The interpretations of an equality expression are the interpretations of the corresponding function 2406 call. 1805 The interpretations of an equality expression are the interpretations of the corresponding function call. 2407 1806 2408 1807 \begin{sloppypar} 2409 The result of an equality comparison between two pointers to predefined functions or predefined 2410 values is implementation-defined. 1808 The result of an equality comparison between two pointers to predefined functions or predefined values is implementation-defined. 2411 1809 \end{sloppypar} 2412 1810 \begin{rationale} 2413 The implementation-defined status of equality comparisons allows implementations to use one library 2414 routine to implement many predefined functions. These optimization are particularly important when 2415 the predefined functions are polymorphic, as is the case for most pointer operations 1811 The implementation-defined status of equality comparisons allows implementations to use one library routine to implement many predefined functions. 1812 These optimization are particularly important when the predefined functions are polymorphic, as is the case for most pointer operations 2416 1813 \end{rationale} 2417 1814 … … 2439 1836 long long unsigned int ?&?( long long unsigned int, long long unsigned int ); 2440 1837 \end{lstlisting} 2441 For every extended integer type \lstinline$X$ with \Index{integer conversion rank} greater than the 2442 rank of \lstinline$int$ there exist 1838 For every extended integer type \lstinline$X$ with \Index{integer conversion rank} greater than the rank of \lstinline$int$ there exist 2443 1839 % Don't use predefined: keep this out of prelude.cf. 2444 1840 \begin{lstlisting} … … 2447 1843 2448 1844 \semantics 2449 The interpretations of a bitwise AND expression are the interpretations of the corresponding 2450 function call. 1845 The interpretations of a bitwise AND expression are the interpretations of the corresponding function call. 2451 1846 2452 1847 … … 2473 1868 long long unsigned int ?^?( long long unsigned int, long long unsigned int ); 2474 1869 \end{lstlisting} 2475 For every extended integer type \lstinline$X$ with \Index{integer conversion rank} greater than the 2476 rank of \lstinline$int$ there exist 1870 For every extended integer type \lstinline$X$ with \Index{integer conversion rank} greater than the rank of \lstinline$int$ there exist 2477 1871 % Don't use predefined: keep this out of prelude.cf. 2478 1872 \begin{lstlisting} … … 2481 1875 2482 1876 \semantics 2483 The interpretations of a bitwise exclusive OR expression are the interpretations of the 2484 corresponding function call. 1877 The interpretations of a bitwise exclusive OR expression are the interpretations of the corresponding function call. 2485 1878 2486 1879 … … 2507 1900 long long unsigned int ?|?( long long unsigned int, long long unsigned int ); 2508 1901 \end{lstlisting} 2509 For every extended integer type \lstinline$X$ with \Index{integer conversion rank} greater than the 2510 rank of \lstinline$int$ there exist 1902 For every extended integer type \lstinline$X$ with \Index{integer conversion rank} greater than the rank of \lstinline$int$ there exist 2511 1903 % Don't use predefined: keep this out of prelude.cf. 2512 1904 \begin{lstlisting} … … 2515 1907 2516 1908 \semantics 2517 The interpretations of a bitwise inclusive OR expression are the interpretations of the 2518 corresponding function call. 1909 The interpretations of a bitwise inclusive OR expression are the interpretations of the corresponding function call. 2519 1910 2520 1911 … … 2528 1919 2529 1920 \semantics The operands of the expression ``\lstinline$a && b$'' are treated as 2530 ``\lstinline$(int)((a)!=0)$'' and ``\lstinline$(int)((b)!=0)$'', which shall both be 2531 unambiguous. The expression has only one interpretation, which is of type \lstinline$int$. 2532 \begin{rationale} 2533 When the operands of a logical expression are values of built-in types, and ``\lstinline$!=$'' has 2534 not been redefined for those types, the compiler can optimize away the function calls. 1921 ``\lstinline$(int)((a)!=0)$'' and ``\lstinline$(int)((b)!=0)$'', which shall both be unambiguous. 1922 The expression has only one interpretation, which is of type \lstinline$int$. 1923 \begin{rationale} 1924 When the operands of a logical expression are values of built-in types, and ``\lstinline$!=$'' has not been redefined for those types, the compiler can optimize away the function calls. 2535 1925 2536 1926 A common C idiom omits comparisons to \lstinline$0$ in the controlling expressions of loops and 2537 \lstinline$if$ statements. For instance, the loop below iterates as long as \lstinline$rp$ points2538 at a \lstinline$Rational$ value that is non-zero.2539 2540 \begin{lstlisting} 2541 extern type Rational;@\use{Rational}@1927 \lstinline$if$ statements. 1928 For instance, the loop below iterates as long as \lstinline$rp$ points at a \lstinline$Rational$ value that is non-zero. 1929 1930 \begin{lstlisting} 1931 extern otype Rational;@\use{Rational}@ 2542 1932 extern const Rational 0;@\use{0}@ 2543 1933 extern int ?!=?( Rational, Rational ); 2544 1934 Rational *rp; 2545 2546 1935 while ( rp && *rp ) { ... } 2547 1936 \end{lstlisting} 2548 The logical expression calls the \lstinline$Rational$ inequality operator, passing 2549 it \lstinline$*rp$ and the \lstinline$Rational 0$, and getting a 1 or 0 as a result. In 2550 contrast, {\CC} would apply a programmer-defined \lstinline$Rational$-to-\lstinline$int$ 2551 conversion to \lstinline$*rp$ in the equivalent situation. The conversion to \lstinline$int$ would 2552 produce a general integer value, which is unfortunate, and possibly dangerous if the conversion was 2553 not written with this situation in mind. 1937 The logical expression calls the \lstinline$Rational$ inequality operator, passing it \lstinline$*rp$ and the \lstinline$Rational 0$, and getting a 1 or 0 as a result. 1938 In contrast, {\CC} would apply a programmer-defined \lstinline$Rational$-to-\lstinline$int$ conversion to \lstinline$*rp$ in the equivalent situation. 1939 The conversion to \lstinline$int$ would produce a general integer value, which is unfortunate, and possibly dangerous if the conversion was not written with this situation in mind. 2554 1940 \end{rationale} 2555 1941 … … 2565 1951 \semantics 2566 1952 2567 The operands of the expression ``\lstinline$a || b$'' are treated as ``\lstinline$(int)((a)!=0)$'' 2568 and ``\lstinline$(int)((b))!=0)$'', which shall both be unambiguous. The expression has only one 2569 interpretation, which is of type \lstinline$int$. 1953 The operands of the expression ``\lstinline$a || b$'' are treated as ``\lstinline$(int)((a)!=0)$'' and ``\lstinline$(int)((b))!=0)$'', which shall both be unambiguous. 1954 The expression has only one interpretation, which is of type \lstinline$int$. 2570 1955 2571 1956 … … 2580 1965 2581 1966 \semantics 2582 In the conditional expression\use{?:} ``\lstinline$a?b:c$'', if the second and 2583 third operands both have an interpretation with \lstinline$void$ type, then the expression has an 2584 interpretation with type \lstinline$void$, equivalent to 1967 In the conditional expression\use{?:} ``\lstinline$a?b:c$'', if the second and third operands both have an interpretation with \lstinline$void$ type, then the expression has an interpretation with type \lstinline$void$, equivalent to 2585 1968 \begin{lstlisting} 2586 1969 ( int)(( a)!=0) ? ( void)( b) : ( void)( c) 2587 1970 \end{lstlisting} 2588 1971 2589 If the second and third operands both have interpretations with non-\lstinline$void$ types, the 2590 expression is treated as if it were the call ``\lstinline$cond((a)!=0, b, c)$'', 2591 with \lstinline$cond$ declared as 2592 \begin{lstlisting} 2593 forall( type T ) T cond( int, T, T ); 2594 2595 forall( dtype D ) void 2596 * cond( int, D *, void * ), 2597 * cond( int, void *, D * ); 2598 2599 forall( dtype D ) _atomic void 2600 * cond( int, _Atomic D *, _Atomic void * ), 2601 * cond( int, _Atomic void *, _Atomic D * ); 2602 2603 forall( dtype D ) const void 2604 * cond( int, const D *, const void * ), 2605 * cond( int, const void *, const D * ); 2606 2607 forall( dtype D ) restrict void 2608 * cond( int, restrict D *, restrict void * ), 2609 * cond( int, restrict void *, restrict D * ); 2610 2611 forall( dtype D ) volatile void 2612 * cond( int, volatile D *, volatile void * ), 2613 * cond( int, volatile void *, volatile D * ); 2614 2615 forall( dtype D ) _Atomic const void 2616 * cond( int, _Atomic const D *, _Atomic const void * ), 2617 * cond( int, _Atomic const void *, _Atomic const D * ); 2618 2619 forall( dtype D ) _Atomic restrict void 2620 * cond( int, _Atomic restrict D *, _Atomic restrict void * ), 2621 * cond( int, _Atomic restrict void *, _Atomic restrict D * ); 2622 2623 forall( dtype D ) _Atomic volatile void 2624 * cond( int, _Atomic volatile D *, _Atomic volatile void * ), 2625 * cond( int, _Atomic volatile void *, _Atomic volatile D * ); 2626 2627 forall( dtype D ) const restrict void 2628 * cond( int, const restrict D *, const restrict void * ), 2629 * cond( int, const restrict void *, const restrict D * ); 2630 2631 forall( dtype D ) const volatile void 2632 * cond( int, const volatile D *, const volatile void * ), 2633 * cond( int, const volatile void *, const volatile D * ); 2634 2635 forall( dtype D ) restrict volatile void 2636 * cond( int, restrict volatile D *, restrict volatile void * ), 2637 * cond( int, restrict volatile void *, restrict volatile D * ); 2638 2639 forall( dtype D ) _Atomic const restrict void 2640 * cond( int, _Atomic const restrict D *, _Atomic const restrict void * ), 1972 If the second and third operands both have interpretations with non-\lstinline$void$ types, the expression is treated as if it were the call ``\lstinline$cond((a)!=0, b, c)$'', with \lstinline$cond$ declared as 1973 \begin{lstlisting} 1974 forall( otype T ) T cond( int, T, T ); 1975 forall( dtype D ) void * cond( int, D *, void * ), * cond( int, void *, D * ); 1976 forall( dtype D ) _atomic void * cond( 1977 int, _Atomic D *, _Atomic void * ), * cond( int, _Atomic void *, _Atomic D * ); 1978 forall( dtype D ) const void * cond( 1979 int, const D *, const void * ), * cond( int, const void *, const D * ); 1980 forall( dtype D ) restrict void * cond( 1981 int, restrict D *, restrict void * ), * cond( int, restrict void *, restrict D * ); 1982 forall( dtype D ) volatile void * cond( 1983 int, volatile D *, volatile void * ), * cond( int, volatile void *, volatile D * ); 1984 forall( dtype D ) _Atomic const void * cond( 1985 int, _Atomic const D *, _Atomic const void * ), * cond( int, _Atomic const void *, _Atomic const D * ); 1986 forall( dtype D ) _Atomic restrict void * cond( 1987 int, _Atomic restrict D *, _Atomic restrict void * ), * cond( int, _Atomic restrict void *, _Atomic restrict D * ); 1988 forall( dtype D ) _Atomic volatile void * cond( 1989 int, _Atomic volatile D *, _Atomic volatile void * ), * cond( int, _Atomic volatile void *, _Atomic volatile D * ); 1990 forall( dtype D ) const restrict void * cond( 1991 int, const restrict D *, const restrict void * ), * cond( int, const restrict void *, const restrict D * ); 1992 forall( dtype D ) const volatile void * cond( 1993 int, const volatile D *, const volatile void * ), * cond( int, const volatile void *, const volatile D * ); 1994 forall( dtype D ) restrict volatile void * cond( 1995 int, restrict volatile D *, restrict volatile void * ), * cond( int, restrict volatile void *, restrict volatile D * ); 1996 forall( dtype D ) _Atomic const restrict void * cond( 1997 int, _Atomic const restrict D *, _Atomic const restrict void * ), 2641 1998 * cond( int, _Atomic const restrict void *, _Atomic const restrict D * ); 2642 2643 forall( dtype D ) _Atomic const volatile void 2644 * cond( int, _Atomic const volatile D *, _Atomic const volatile void * ), 1999 forall( dtype D ) _Atomic const volatile void * cond( 2000 int, _Atomic const volatile D *, _Atomic const volatile void * ), 2645 2001 * cond( int, _Atomic const volatile void *, _Atomic const volatile D * ); 2646 2647 forall( dtype D ) _Atomic restrict volatile void 2648 * cond( int, _Atomic restrict volatile D *, 2649 _Atomic restrict volatile void * ), 2650 * cond( int, _Atomic restrict volatile void *, 2651 _Atomic restrict volatile D * ); 2652 2653 forall( dtype D ) const restrict volatile void 2654 * cond( int, const restrict volatile D *, 2655 const restrict volatile void * ), 2656 * cond( int, const restrict volatile void *, 2657 const restrict volatile D * ); 2658 2659 forall( dtype D ) _Atomic const restrict volatile void 2660 * cond( int, _Atomic const restrict volatile D *, 2661 _Atomic const restrict volatile void * ), 2662 * cond( int, _Atomic const restrict volatile void *, 2663 _Atomic const restrict volatile D * ); 2664 \end{lstlisting} 2665 2666 \begin{rationale} 2667 The object of the above is to apply the \Index{usual arithmetic conversion}s when the second and 2668 third operands have arithmetic type, and to combine the qualifiers of the second and third operands 2669 if they are pointers. 2002 forall( dtype D ) _Atomic restrict volatile void * cond( 2003 int, _Atomic restrict volatile D *, _Atomic restrict volatile void * ), 2004 * cond( int, _Atomic restrict volatile void *, _Atomic restrict volatile D * ); 2005 forall( dtype D ) const restrict volatile void * cond( 2006 int, const restrict volatile D *, const restrict volatile void * ), 2007 * cond( int, const restrict volatile void *, const restrict volatile D * ); 2008 forall( dtype D ) _Atomic const restrict volatile void * cond( 2009 int, _Atomic const restrict volatile D *, _Atomic const restrict volatile void * ), 2010 * cond( int, _Atomic const restrict volatile void *, _Atomic const restrict volatile D * ); 2011 \end{lstlisting} 2012 2013 \begin{rationale} 2014 The object of the above is to apply the \Index{usual arithmetic conversion}s when the second and third operands have arithmetic type, and to combine the qualifiers of the second and third operands if they are pointers. 2670 2015 \end{rationale} 2671 2016 … … 2685 2030 rand() ? cip : vip; 2686 2031 \end{lstlisting} 2687 The expression has type \lstinline$const volatile int *$, with safe conversions applied to the second 2688 and third operands to add \lstinline$volatile$ and \lstinline$const$ qualifiers, respectively. 2032 The expression has type \lstinline$const volatile int *$, with safe conversions applied to the second and third operands to add \lstinline$volatile$ and \lstinline$const$ qualifiers, respectively. 2689 2033 2690 2034 \begin{lstlisting} … … 2708 2052 2709 2053 \rewriterules 2710 Let ``\(\leftarrow\)'' be any of the assignment operators. Then 2054 Let ``\(\leftarrow\)'' be any of the assignment operators. 2055 Then 2711 2056 \use{?=?}\use{?*=?}\use{?/=?}\use{?%=?}\use{?+=?}\use{?-=?} 2712 2057 \use{?>>=?}\use{?&=?}\use{?^=?}\use{?"|=?}%use{?<<=?} … … 2716 2061 2717 2062 \semantics 2718 Each interpretation of the left operand of an assignment expression is considered separately. For 2719 each interpretation that is a bit-field or is declared with the \lstinline$register$ storage class 2720 specifier, the expression has one valid interpretation, with the type of the left operand. The 2721 right operand is cast to that type, and the assignment expression is ambiguous if either operand is. 2722 For the remaining interpretations, the expression is rewritten, and the interpretations of the 2723 assignment expression are the interpretations of the corresponding function call. Finally, all 2724 interpretations of the expression produced for the different interpretations of the left operand are 2725 combined to produce the interpretations of the expression as a whole; where interpretations have 2726 compatible result types, the best interpretations are selected in the manner described for function 2727 call expressions. 2063 Each interpretation of the left operand of an assignment expression is considered separately. 2064 For each interpretation that is a bit-field or is declared with the \lstinline$register$ storage class specifier, the expression has one valid interpretation, with the type of the left operand. 2065 The right operand is cast to that type, and the assignment expression is ambiguous if either operand is. 2066 For the remaining interpretations, the expression is rewritten, and the interpretations of the assignment expression are the interpretations of the corresponding function call. 2067 Finally, all interpretations of the expression produced for the different interpretations of the left operand are combined to produce the interpretations of the expression as a whole; 2068 where interpretations have compatible result types, the best interpretations are selected in the manner described for function call expressions. 2728 2069 2729 2070 … … 2790 2131 ?=?( volatile _Complex long double *, _Complex long double ), 2791 2132 ?=?( _Atomic volatile _Complex long double *, _Atomic _Complex long double ); 2792 2793 2133 forall( ftype FT ) FT 2794 2134 * ?=?( FT * volatile *, FT * ), 2795 2135 * ?=?( FT * volatile *, forall( ftype F ) F * ); 2796 2797 2136 forall( ftype FT ) FT const 2798 2137 * ?=?( FT const * volatile *, FT const * ), 2799 2138 * ?=?( FT const * volatile *, forall( ftype F ) F * ); 2800 2801 2139 forall( ftype FT ) FT volatile 2802 2140 * ?=?( FT volatile * volatile *, FT * ), 2803 2141 * ?=?( FT volatile * volatile *, forall( ftype F ) F * ); 2804 2805 2142 forall( ftype FT ) FT const 2806 2143 * ?=?( FT const volatile * volatile *, FT const * ), 2807 2144 * ?=?( FT const volatile * volatile *, forall( ftype F ) F * ); 2808 2809 2145 forall( dtype DT ) DT 2810 2146 * ?=?( DT * restrict volatile *, DT * ), … … 2814 2150 * ?=?( DT * _Atomic restrict volatile *, void * ), 2815 2151 * ?=?( DT * _Atomic restrict volatile *, forall( dtype D ) D * ); 2816 2817 2152 forall( dtype DT ) DT _Atomic 2818 2153 * ?=?( _Atomic DT * restrict volatile *, DT _Atomic * ), … … 2822 2157 * ?=?( _Atomic DT * _Atomic restrict volatile *, void * ), 2823 2158 * ?=?( _Atomic DT * _Atomic restrict volatile *, forall( dtype D ) D * ); 2824 2825 2159 forall( dtype DT ) DT const 2826 2160 * ?=?( DT const * restrict volatile *, DT const * ), … … 2830 2164 * ?=?( DT const * _Atomic restrict volatile *, void const * ), 2831 2165 * ?=?( DT const * _Atomic restrict volatile *, forall( dtype D ) D * ); 2832 2833 2166 forall( dtype DT ) DT restrict 2834 2167 * ?=?( restrict DT * restrict volatile *, DT restrict * ), … … 2838 2171 * ?=?( restrict DT * _Atomic restrict volatile *, void * ), 2839 2172 * ?=?( restrict DT * _Atomic restrict volatile *, forall( dtype D ) D * ); 2840 2841 2173 forall( dtype DT ) DT volatile 2842 2174 * ?=?( DT volatile * restrict volatile *, DT volatile * ), … … 2846 2178 * ?=?( DT volatile * _Atomic restrict volatile *, void volatile * ), 2847 2179 * ?=?( DT volatile * _Atomic restrict volatile *, forall( dtype D ) D * ); 2848 2849 2180 forall( dtype DT ) DT _Atomic const 2850 2181 * ?=?( DT _Atomic const * restrict volatile *, DT _Atomic const * ), … … 2854 2185 * ?=?( DT _Atomic const * _Atomic restrict volatile *, void const * ), 2855 2186 * ?=?( DT _Atomic const * _Atomic restrict volatile *, forall( dtype D ) D * ); 2856 2857 2187 forall( dtype DT ) DT _Atomic restrict 2858 2188 * ?=?( _Atomic restrict DT * restrict volatile *, DT _Atomic restrict * ), … … 2862 2192 * ?=?( _Atomic restrict DT * _Atomic restrict volatile *, void * ), 2863 2193 * ?=?( _Atomic restrict DT * _Atomic restrict volatile *, forall( dtype D ) D * ); 2864 2865 2194 forall( dtype DT ) DT _Atomic volatile 2866 2195 * ?=?( DT _Atomic volatile * restrict volatile *, DT _Atomic volatile * ), … … 2870 2199 * ?=?( DT _Atomic volatile * _Atomic restrict volatile *, void volatile * ), 2871 2200 * ?=?( DT _Atomic volatile * _Atomic restrict volatile *, forall( dtype D ) D * ); 2872 2873 2201 forall( dtype DT ) DT const restrict 2874 2202 * ?=?( DT const restrict * restrict volatile *, DT const restrict * ), … … 2878 2206 * ?=?( DT const restrict * _Atomic restrict volatile *, void const * ), 2879 2207 * ?=?( DT const restrict * _Atomic restrict volatile *, forall( dtype D ) D * ); 2880 2881 2208 forall( dtype DT ) DT const volatile 2882 2209 * ?=?( DT const volatile * restrict volatile *, DT const volatile * ), … … 2886 2213 * ?=?( DT const volatile * _Atomic restrict volatile *, void const volatile * ), 2887 2214 * ?=?( DT const volatile * _Atomic restrict volatile *, forall( dtype D ) D * ); 2888 2889 2215 forall( dtype DT ) DT restrict volatile 2890 2216 * ?=?( DT restrict volatile * restrict volatile *, DT restrict volatile * ), … … 2894 2220 * ?=?( DT restrict volatile * _Atomic restrict volatile *, void volatile * ), 2895 2221 * ?=?( DT restrict volatile * _Atomic restrict volatile *, forall( dtype D ) D * ); 2896 2897 2222 forall( dtype DT ) DT _Atomic const restrict 2898 2223 * ?=?( DT _Atomic const restrict * restrict volatile *, … … 2908 2233 * ?=?( DT _Atomic const restrict * _Atomic restrict volatile *, 2909 2234 forall( dtype D ) D * ); 2910 2911 2235 forall( dtype DT ) DT _Atomic const volatile 2912 2236 * ?=?( DT _Atomic const volatile * restrict volatile *, … … 2922 2246 * ?=?( DT _Atomic const volatile * _Atomic restrict volatile *, 2923 2247 forall( dtype D ) D * ); 2924 2925 2248 forall( dtype DT ) DT _Atomic restrict volatile 2926 2249 * ?=?( DT _Atomic restrict volatile * restrict volatile *, … … 2936 2259 * ?=?( DT _Atomic restrict volatile * _Atomic restrict volatile *, 2937 2260 forall( dtype D ) D * ); 2938 2939 2261 forall( dtype DT ) DT const restrict volatile 2940 2262 * ?=?( DT const restrict volatile * restrict volatile *, … … 2950 2272 * ?=?( DT const restrict volatile * _Atomic restrict volatile *, 2951 2273 forall( dtype D ) D * ); 2952 2953 2274 forall( dtype DT ) DT _Atomic const restrict volatile 2954 2275 * ?=?( DT _Atomic const restrict volatile * restrict volatile *, … … 2964 2285 * ?=?( DT _Atomic const restrict volatile * _Atomic restrict volatile *, 2965 2286 forall( dtype D ) D * ); 2966 2967 2287 forall( dtype DT ) void 2968 2288 * ?=?( void * restrict volatile *, DT * ); 2969 2970 2289 forall( dtype DT ) void const 2971 2290 * ?=?( void const * restrict volatile *, DT const * ); 2972 2973 2291 forall( dtype DT ) void volatile 2974 2292 * ?=?( void volatile * restrict volatile *, DT volatile * ); 2975 2976 2293 forall( dtype DT ) void const volatile 2977 2294 * ?=?( void const volatile * restrict volatile *, DT const volatile * ); 2978 2295 \end{lstlisting} 2979 2296 \begin{rationale} 2980 The pattern of overloadings for simple assignment resembles that of pointer increment and decrement, 2981 except that the polymorphic pointer assignment functions declare a \lstinline$dtype$ parameter, 2982 instead of a \lstinline$type$ parameter, because the left operand may be a pointer to an incomplete 2983 type. 2297 The pattern of overloadings for simple assignment resembles that of pointer increment and decrement, except that the polymorphic pointer assignment functions declare a \lstinline$dtype$ parameter, instead of a \lstinline$type$ parameter, because the left operand may be a pointer to an incomplete type. 2984 2298 \end{rationale} 2985 2299 … … 3006 2320 3007 2321 \semantics 3008 The structure assignment functions provide member-wise assignment; each non-array member and each 3009 element of each array member of the right argument is assigned to the corresponding member or 3010 element of the left argument using the assignment function defined for its type. All other 3011 assignment functions have the same effect as the corresponding C assignment expression. 3012 \begin{rationale} 3013 Note that, by default, union assignment\index{deficiencies!union assignment} uses C semantics---that 3014 is, bitwise copy---even if some of the union members have programmer-defined assignment functions. 2322 The structure assignment functions provide member-wise assignment; 2323 each non-array member and each element of each array member of the right argument is assigned to the corresponding member or element of the left argument using the assignment function defined for its type. 2324 All other assignment functions have the same effect as the corresponding C assignment expression. 2325 \begin{rationale} 2326 Note that, by default, union assignment\index{deficiencies!union assignment} uses C semantics---that is, bitwise copy---even if some of the union members have programmer-defined assignment functions. 3015 2327 \end{rationale} 3016 2328 … … 3020 2332 \predefined 3021 2333 \begin{lstlisting} 3022 forall( type T ) T2334 forall( otype T ) T 3023 2335 * ?+=?( T * restrict volatile *, ptrdiff_t ), 3024 2336 * ?-=?( T * restrict volatile *, ptrdiff_t ), 3025 2337 * ?+=?( T * _Atomic restrict volatile *, ptrdiff_t ), 3026 2338 * ?-=?( T * _Atomic restrict volatile *, ptrdiff_t ); 3027 3028 forall( type T ) T _Atomic 2339 forall( otype T ) T _Atomic 3029 2340 * ?+=?( T _Atomic * restrict volatile *, ptrdiff_t ), 3030 2341 * ?-=?( T _Atomic * restrict volatile *, ptrdiff_t ), 3031 2342 * ?+=?( T _Atomic * _Atomic restrict volatile *, ptrdiff_t ), 3032 2343 * ?-=?( T _Atomic * _Atomic restrict volatile *, ptrdiff_t ); 3033 3034 forall( type T ) T const 2344 forall( otype T ) T const 3035 2345 * ?+=?( T const * restrict volatile *, ptrdiff_t ), 3036 2346 * ?-=?( T const * restrict volatile *, ptrdiff_t ), 3037 2347 * ?+=?( T const * _Atomic restrict volatile *, ptrdiff_t ), 3038 2348 * ?-=?( T const * _Atomic restrict volatile *, ptrdiff_t ); 3039 3040 forall( type T ) T restrict 2349 forall( otype T ) T restrict 3041 2350 * ?+=?( T restrict * restrict volatile *, ptrdiff_t ), 3042 2351 * ?-=?( T restrict * restrict volatile *, ptrdiff_t ), 3043 2352 * ?+=?( T restrict * _Atomic restrict volatile *, ptrdiff_t ), 3044 2353 * ?-=?( T restrict * _Atomic restrict volatile *, ptrdiff_t ); 3045 3046 forall( type T ) T volatile 2354 forall( otype T ) T volatile 3047 2355 * ?+=?( T volatile * restrict volatile *, ptrdiff_t ), 3048 2356 * ?-=?( T volatile * restrict volatile *, ptrdiff_t ), 3049 2357 * ?+=?( T volatile * _Atomic restrict volatile *, ptrdiff_t ), 3050 2358 * ?-=?( T volatile * _Atomic restrict volatile *, ptrdiff_t ); 3051 3052 forall( type T ) T _Atomic const 2359 forall( otype T ) T _Atomic const 3053 2360 * ?+=?( T _Atomic const restrict volatile *, ptrdiff_t ), 3054 2361 * ?-=?( T _Atomic const restrict volatile *, ptrdiff_t ), 3055 2362 * ?+=?( T _Atomic const _Atomic restrict volatile *, ptrdiff_t ), 3056 2363 * ?-=?( T _Atomic const _Atomic restrict volatile *, ptrdiff_t ); 3057 3058 forall( type T ) T _Atomic restrict 2364 forall( otype T ) T _Atomic restrict 3059 2365 * ?+=?( T _Atomic restrict * restrict volatile *, ptrdiff_t ), 3060 2366 * ?-=?( T _Atomic restrict * restrict volatile *, ptrdiff_t ), 3061 2367 * ?+=?( T _Atomic restrict * _Atomic restrict volatile *, ptrdiff_t ), 3062 2368 * ?-=?( T _Atomic restrict * _Atomic restrict volatile *, ptrdiff_t ); 3063 3064 forall( type T ) T _Atomic volatile 2369 forall( otype T ) T _Atomic volatile 3065 2370 * ?+=?( T _Atomic volatile * restrict volatile *, ptrdiff_t ), 3066 2371 * ?-=?( T _Atomic volatile * restrict volatile *, ptrdiff_t ), 3067 2372 * ?+=?( T _Atomic volatile * _Atomic restrict volatile *, ptrdiff_t ), 3068 2373 * ?-=?( T _Atomic volatile * _Atomic restrict volatile *, ptrdiff_t ); 3069 3070 forall( type T ) T const restrict 2374 forall( otype T ) T const restrict 3071 2375 * ?+=?( T const restrict * restrict volatile *, ptrdiff_t ), 3072 2376 * ?-=?( T const restrict * restrict volatile *, ptrdiff_t ), 3073 2377 * ?+=?( T const restrict * _Atomic restrict volatile *, ptrdiff_t ), 3074 2378 * ?-=?( T const restrict * _Atomic restrict volatile *, ptrdiff_t ); 3075 3076 forall( type T ) T const volatile 2379 forall( otype T ) T const volatile 3077 2380 * ?+=?( T const volatile * restrict volatile *, ptrdiff_t ), 3078 2381 * ?-=?( T const volatile * restrict volatile *, ptrdiff_t ), 3079 2382 * ?+=?( T const volatile * _Atomic restrict volatile *, ptrdiff_t ), 3080 2383 * ?-=?( T const volatile * _Atomic restrict volatile *, ptrdiff_t ); 3081 3082 forall( type T ) T restrict volatile 2384 forall( otype T ) T restrict volatile 3083 2385 * ?+=?( T restrict volatile * restrict volatile *, ptrdiff_t ), 3084 2386 * ?-=?( T restrict volatile * restrict volatile *, ptrdiff_t ), 3085 2387 * ?+=?( T restrict volatile * _Atomic restrict volatile *, ptrdiff_t ), 3086 2388 * ?-=?( T restrict volatile * _Atomic restrict volatile *, ptrdiff_t ); 3087 3088 forall( type T ) T _Atomic const restrict 2389 forall( otype T ) T _Atomic const restrict 3089 2390 * ?+=?( T _Atomic const restrict * restrict volatile *, ptrdiff_t ), 3090 2391 * ?-=?( T _Atomic const restrict * restrict volatile *, ptrdiff_t ), 3091 2392 * ?+=?( T _Atomic const restrict * _Atomic restrict volatile *, ptrdiff_t ), 3092 2393 * ?-=?( T _Atomic const restrict * _Atomic restrict volatile *, ptrdiff_t ); 3093 3094 forall( type T ) T _Atomic const volatile 2394 forall( otype T ) T _Atomic const volatile 3095 2395 * ?+=?( T _Atomic const volatile * restrict volatile *, ptrdiff_t ), 3096 2396 * ?-=?( T _Atomic const volatile * restrict volatile *, ptrdiff_t ), 3097 2397 * ?+=?( T _Atomic const volatile * _Atomic restrict volatile *, ptrdiff_t ), 3098 2398 * ?-=?( T _Atomic const volatile * _Atomic restrict volatile *, ptrdiff_t ); 3099 3100 forall( type T ) T _Atomic restrict volatile 2399 forall( otype T ) T _Atomic restrict volatile 3101 2400 * ?+=?( T _Atomic restrict volatile * restrict volatile *, ptrdiff_t ), 3102 2401 * ?-=?( T _Atomic restrict volatile * restrict volatile *, ptrdiff_t ), 3103 2402 * ?+=?( T _Atomic restrict volatile * _Atomic restrict volatile *, ptrdiff_t ), 3104 2403 * ?-=?( T _Atomic restrict volatile * _Atomic restrict volatile *, ptrdiff_t ); 3105 3106 forall( type T ) T const restrict volatile 2404 forall( otype T ) T const restrict volatile 3107 2405 * ?+=?( T const restrict volatile * restrict volatile *, ptrdiff_t ), 3108 2406 * ?-=?( T const restrict volatile * restrict volatile *, ptrdiff_t ), 3109 2407 * ?+=?( T const restrict volatile * _Atomic restrict volatile *, ptrdiff_t ), 3110 2408 * ?-=?( T const restrict volatile * _Atomic restrict volatile *, ptrdiff_t ); 3111 3112 forall( type T ) T _Atomic const restrict volatile 2409 forall( otype T ) T _Atomic const restrict volatile 3113 2410 * ?+=?( T _Atomic const restrict volatile * restrict volatile *, ptrdiff_t ), 3114 2411 * ?-=?( T _Atomic const restrict volatile * restrict volatile *, ptrdiff_t ), … … 3321 2618 \semantics 3322 2619 In the comma expression ``\lstinline$a, b$'', the first operand is interpreted as 3323 ``\lstinline$( void )(a)$'', which shall be unambiguous\index{ambiguous interpretation}. The3324 interpretations of the expression are the interpretations of the second operand.2620 ``\lstinline$( void )(a)$'', which shall be unambiguous\index{ambiguous interpretation}. 2621 The interpretations of the expression are the interpretations of the second operand. 3325 2622 3326 2623 … … 3337 2634 3338 2635 \constraints 3339 If an identifier has \Index{no linkage}, there shall be no more than one declaration of the 3340 identifier ( in a declarator or type specifier ) with compatible types in the same scope and in the 3341 same name space, except that: 2636 If an identifier has \Index{no linkage}, there shall be no more than one declaration of the identifier ( in a declarator or type specifier ) with compatible types in the same scope and in the same name space, except that: 3342 2637 \begin{itemize} 3343 \item 3344 a typedef name may be redefined to denote the same type as it currently does, provided that type is 3345 not a variably modified type; 3346 \item 3347 tags may be redeclared as specified in section 6.7.2.3 of the {\c11} standard. 2638 \item a typedef name may be redefined to denote the same type as it currently does, provided that type is not a variably modified type; 2639 \item tags may be redeclared as specified in section 6.7.2.3 of the {\c11} standard. 3348 2640 \end{itemize} 3349 2641 \begin{rationale} 3350 This constraint adds the phrase ``with compatible types'' to the {\c11} constraint, to allow 3351 overloading. 3352 \end{rationale} 3353 3354 An identifier declared by a type declaration shall not be redeclared as a parameter in a function 3355 definition whose declarator includes an identifier list. 3356 \begin{rationale} 3357 This restriction echos {\c11}'s ban on the redeclaration of typedef names as parameters. This 3358 avoids an ambiguity between old-style function declarations and new-style function prototypes: 2642 This constraint adds the phrase ``with compatible types'' to the {\c11} constraint, to allow overloading. 2643 \end{rationale} 2644 2645 An identifier declared by a type declaration shall not be redeclared as a parameter in a function definition whose declarator includes an identifier list. 2646 \begin{rationale} 2647 This restriction echos {\c11}'s ban on the redeclaration of typedef names as parameters. 2648 This avoids an ambiguity between old-style function declarations and new-style function prototypes: 3359 2649 \begin{lstlisting} 3360 2650 void f( Complex, // ... 3000 characters ... 3361 2651 void g( Complex, // ... 3000 characters ... 3362 int Complex; { ... }3363 \end{lstlisting}3364 Without the rule, \lstinline$Complex$ would be a type in the first case, and a parameter name in the 3365 second.2652 int Complex; 2653 { ... } 2654 \end{lstlisting} 2655 Without the rule, \lstinline$Complex$ would be a type in the first case, and a parameter name in the second. 3366 2656 \end{rationale} 3367 2657 … … 3382 2672 3383 2673 \semantics 3384 \CFA extends the {\c11} definition of \define{anonymous structure} to include structure 3385 specifiers with tags, and extends the {\c11} definition of \define{anonymous union} to include union 3386 specifiers with tags. 2674 \CFA extends the {\c11} definition of \define{anonymous structure} to include structure specifiers with tags, and extends the {\c11} definition of \define{anonymous union} to include union specifiers with tags. 3387 2675 \begin{rationale} 3388 2676 This extension imitates an extension in the Plan 9 C compiler \cite{Thompson90new}. … … 3401 2689 cp.x = 0; 3402 2690 cp.color = RED; 3403 3404 2691 struct literal {@\impl{literal}@ 3405 2692 enum { NUMBER, STRING } tag; 3406 2693 union { 3407 double n;3408 char *s;2694 double n; 2695 char *s; 3409 2696 }; 3410 2697 }; … … 3428 2715 \begin{comment} 3429 2716 \constraints 3430 If the \nonterm{declaration-specifiers} of a declaration that contains a \nonterm{forall-specifier} 3431 declares a structure or union tag, the types of the members of the structure or union shall not use 3432 any of the type identifiers declared by the \nonterm{type-parameter-list}. 3433 \begin{rationale} 3434 This sort of declaration is illegal because the scope of the type identifiers ends at the end of the 3435 declaration, but the scope of the structure tag does not. 3436 \begin{lstlisting} 3437 forall( type T ) struct Pair { T a, b; } mkPair( T, T ); // illegal 3438 \end{lstlisting} 3439 If an instance of \lstinline$struct Pair$ was declared later in the current scope, what would the 3440 members' type be? 2717 If the \nonterm{declaration-specifiers} of a declaration that contains a \nonterm{forall-specifier} declares a structure or union tag, the types of the members of the structure or union shall not use any of the type identifiers declared by the \nonterm{type-parameter-list}. 2718 \begin{rationale} 2719 This sort of declaration is illegal because the scope of the type identifiers ends at the end of the declaration, but the scope of the structure tag does not. 2720 \begin{lstlisting} 2721 forall( otype T ) struct Pair { T a, b; 2722 } mkPair( T, T ); // illegal 2723 \end{lstlisting} 2724 If an instance of \lstinline$struct Pair$ was declared later in the current scope, what would the members' type be? 3441 2725 \end{rationale} 3442 2726 \end{comment} 3443 2727 3444 2728 \semantics 3445 The \nonterm{type-parameter-list}s and assertions of the \nonterm{forall-specifier}s declare type 3446 identifiers, function and object identifiers with \Index{no linkage}. 2729 The \nonterm{type-parameter-list}s and assertions of the \nonterm{forall-specifier}s declare type identifiers, function and object identifiers with \Index{no linkage}. 3447 2730 3448 2731 If, in the declaration ``\lstinline$T D$'', \lstinline$T$ contains \nonterm{forall-specifier}s and … … 3450 2733 \begin{lstlisting} 3451 2734 D( @\normalsize\nonterm{parameter-type-list}@ ) 3452 \end{lstlisting} 3453 then a type identifier declared by one of the \nonterm{forall-specifier}s is an \define{inferred 3454 parameter} of the function declarator if and only if it is not an inferred parameter of a function 3455 declarator in \lstinline$D$, and it is used in the type of a parameter in the following 2735 \end{lstlisting} then a type identifier declared by one of the \nonterm{forall-specifier}s is an \define{inferred parameter} of the function declarator if and only if it is not an inferred parameter of a function declarator in \lstinline$D$, and it is used in the type of a parameter in the following 3456 2736 \nonterm{type-parameter-list} or it and an inferred parameter are used as arguments of a 3457 \Index{specification} in one of the \nonterm{forall-specifier}s. The identifiers declared by 3458 assertions that use an inferred parameter of a function declarator are \Index{assertion parameter}s 3459 of that function declarator. 2737 \Index{specification} in one of the \nonterm{forall-specifier}s. 2738 The identifiers declared by assertions that use an inferred parameter of a function declarator are \Index{assertion parameter}s of that function declarator. 3460 2739 3461 2740 \begin{comment} 3462 2741 \begin{rationale} 3463 Since every inferred parameter is used by some parameter, inference can be understood as a single 3464 bottom-up pass over the expression tree, that only needs to apply local reasoning at each node. 2742 Since every inferred parameter is used by some parameter, inference can be understood as a single bottom-up pass over the expression tree, that only needs to apply local reasoning at each node. 3465 2743 3466 2744 If this restriction were lifted, it would be possible to write 3467 2745 \begin{lstlisting} 3468 forall( type T ) T * alloc( void );@\use{alloc}@ 3469 int *p = alloc(); 2746 forall( otype T ) T * alloc( void );@\use{alloc}@ int *p = alloc(); 3470 2747 \end{lstlisting} 3471 2748 Here \lstinline$alloc()$ would receive \lstinline$int$ as an inferred argument, and return an 3472 \lstinline$int *$. In general, if a call to \lstinline$alloc()$ is a subexpression of an expression 3473 involving polymorphic functions and overloaded identifiers, there could be considerable distance 3474 between the call and the subexpression that causes \lstinline$T$ to be bound. 2749 \lstinline$int *$. 2750 In general, if a call to \lstinline$alloc()$ is a subexpression of an expression involving polymorphic functions and overloaded identifiers, there could be considerable distance between the call and the subexpression that causes \lstinline$T$ to be bound. 3475 2751 3476 2752 With the current restriction, \lstinline$alloc()$ must be given an argument that determines 3477 2753 \lstinline$T$: 3478 2754 \begin{lstlisting} 3479 forall( type T ) T * alloc( T initial_value );@\use{alloc}@2755 forall( otype T ) T * alloc( T initial_value );@\use{alloc}@ 3480 2756 \end{lstlisting} 3481 2757 \end{rationale} 3482 2758 \end{comment} 3483 2759 3484 If a function declarator is part of a function definition, its inferred parameters and assertion 3485 parameters have \Index{block scope};otherwise, identifiers declared by assertions have a2760 If a function declarator is part of a function definition, its inferred parameters and assertion parameters have \Index{block scope}; 2761 otherwise, identifiers declared by assertions have a 3486 2762 \define{declaration scope}, which terminates at the end of the \nonterm{declaration}. 3487 2763 3488 2764 A function type that has at least one inferred parameter is a \define{polymorphic function} type. 3489 Function types with no inferred parameters are \define{monomorphic function} types. One function 3490 type is \define{less polymorphic} than another if it has fewer inferred parameters, or if it has the 3491 same number of inferred parameters and fewer of its explicit parameters have types that depend on an 3492 inferred parameter. 3493 3494 The names of inferred parameters and the order of identifiers in forall specifiers are not relevant 3495 to polymorphic function type compatibility. Let $f$ and $g$ be two polymorphic function types with 3496 the same number of inferred parameters, and let $f_i$ and $g_i$ be the inferred parameters of $f$ 3497 and $g$ in their order of occurance in the function types' \nonterm{parameter-type-list}s. Let $f'$ 3498 be $f$ with every occurrence of $f_i$ replaced by $g_i$, for all $i$. Then $f$ and $g$ are 3499 \Index{compatible type}s if $f'$'s and $g$'s return types and parameter lists are compatible, and if 3500 for every assertion parameter of $f'$ there is an assertion parameter in $g$ with the same 3501 identifier and compatible type, and vice versa. 2765 Function types with no inferred parameters are \define{monomorphic function} types. 2766 One function type is \define{less polymorphic} than another if it has fewer inferred parameters, or if it has the same number of inferred parameters and fewer of its explicit parameters have types that depend on an inferred parameter. 2767 2768 The names of inferred parameters and the order of identifiers in forall specifiers are not relevant to polymorphic function type compatibility. 2769 Let $f$ and $g$ be two polymorphic function types with the same number of inferred parameters, and let $f_i$ and $g_i$ be the inferred parameters of $f$ and $g$ in their order of occurance in the function types' \nonterm{parameter-type-list}s. 2770 Let $f'$ be $f$ with every occurrence of $f_i$ replaced by $g_i$, for all $i$. 2771 Then $f$ and $g$ are 2772 \Index{compatible type}s if $f'$'s and $g$'s return types and parameter lists are compatible, and if for every assertion parameter of $f'$ there is an assertion parameter in $g$ with the same identifier and compatible type, and vice versa. 3502 2773 3503 2774 \examples … … 3505 2776 \begin{lstlisting} 3506 2777 int fi( int ); 3507 forall( type T ) T fT( T );2778 forall( otype T ) T fT( T ); 3508 2779 \end{lstlisting} 3509 2780 \lstinline$fi()$ takes an \lstinline$int$ and returns an \lstinline$int$. \lstinline$fT()$ takes a … … 3511 2782 \begin{lstlisting} 3512 2783 int (*pfi )( int ) = fi; 3513 forall( type T ) T (*pfT )( T ) = fT; 3514 \end{lstlisting} 3515 \lstinline$pfi$ and \lstinline$pfT$ are pointers to functions. \lstinline$pfT$ is not 3516 polymorphic, but the function it points at is. 2784 forall( otype T ) T (*pfT )( T ) = fT; 2785 \end{lstlisting} 2786 \lstinline$pfi$ and \lstinline$pfT$ are pointers to functions. \lstinline$pfT$ is not polymorphic, but the function it points at is. 3517 2787 \begin{lstlisting} 3518 2788 int (*fvpfi( void ))( int ) { 3519 2789 return pfi; 3520 2790 } 3521 forall( type T ) T (*fvpfT( void ))( T ) {2791 forall( otype T ) T (*fvpfT( void ))( T ) { 3522 2792 return pfT; 3523 2793 } 3524 2794 \end{lstlisting} 3525 \lstinline$fvpfi()$ and \lstinline$fvpfT()$ are functions taking no arguments and returning pointers 3526 to functions. \lstinline$fvpfT()$ is monomorphic, but the function that its return value points 3527 at is polymorphic. 3528 \begin{lstlisting} 3529 forall( type T ) int ( *fTpfi( T ) )( int ); 3530 forall( type T ) T ( *fTpfT( T ) )( T ); 3531 forall( type T, type U ) U ( *fTpfU( T ) )( U ); 3532 \end{lstlisting} 3533 \lstinline$fTpfi()$ is a polymorphic function that returns a pointer to a monomorphic function 3534 taking an integer and returning an integer. It could return \lstinline$pfi$. \lstinline$fTpfT()$ 3535 is subtle: it is a polymorphic function returning a \emph{monomorphic} function taking and returning 3536 \lstinline$T$, where \lstinline$T$ is an inferred parameter of \lstinline$fTpfT()$. For instance, 3537 in the expression ``\lstinline$fTpfT(17)$'', \lstinline$T$ is inferred to be \lstinline$int$, and 3538 the returned value would have type \lstinline$int ( * )( int )$. ``\lstinline$fTpfT(17)(13)$'' and 2795 \lstinline$fvpfi()$ and \lstinline$fvpfT()$ are functions taking no arguments and returning pointers to functions. \lstinline$fvpfT()$ is monomorphic, but the function that its return value points at is polymorphic. 2796 \begin{lstlisting} 2797 forall( otype T ) int ( *fTpfi( T ) )( int ); 2798 forall( otype T ) T ( *fTpfT( T ) )( T ); 2799 forall( otype T, otype U ) U ( *fTpfU( T ) )( U ); 2800 \end{lstlisting} 2801 \lstinline$fTpfi()$ is a polymorphic function that returns a pointer to a monomorphic function taking an integer and returning an integer. 2802 It could return \lstinline$pfi$. \lstinline$fTpfT()$ is subtle: it is a polymorphic function returning a \emph{monomorphic} function taking and returning 2803 \lstinline$T$, where \lstinline$T$ is an inferred parameter of \lstinline$fTpfT()$. 2804 For instance, in the expression ``\lstinline$fTpfT(17)$'', \lstinline$T$ is inferred to be \lstinline$int$, and the returned value would have type \lstinline$int ( * )( int )$. ``\lstinline$fTpfT(17)(13)$'' and 3539 2805 ``\lstinline$fTpfT("yes")("no")$'' are legal, but ``\lstinline$fTpfT(17)("no")$'' is illegal. 3540 \lstinline$fTpfU()$ is polymorphic ( in type \lstinline$T$), and returns a pointer to a function that 3541 is polymorphic ( in type \lstinline$U$). ``\lstinline$f5(17)("no")$'' is a legal expression of type 2806 \lstinline$fTpfU()$ is polymorphic ( in type \lstinline$T$), and returns a pointer to a function that is polymorphic ( in type \lstinline$U$). ``\lstinline$f5(17)("no")$'' is a legal expression of type 3542 2807 \lstinline$char *$. 3543 2808 \begin{lstlisting} 3544 forall( type T, type U, type V ) U * f( T *, U, V * const ); 3545 forall( type U, type V, type W ) U * g( V *, U, W * const ); 3546 \end{lstlisting} 3547 The functions \lstinline$f()$ and \lstinline$g()$ have compatible types. Let \(f\) and \(g\) be 3548 their types; then \(f_1\) = \lstinline$T$, \(f_2\) = \lstinline$U$, \(f_3\) = \lstinline$V$, \(g_1\) 3549 = \lstinline$V$, \(g_2\) = \lstinline$U$, and \(g_3\) = \lstinline$W$. Replacing every \(f_i\) 3550 by \(g_i\) in \(f\) gives 3551 \begin{lstlisting} 3552 forall( type V, type U, type W ) U * f( V *, U, W * const ); 3553 \end{lstlisting} 3554 which has a return type and parameter list that is compatible with \(g\). 3555 \begin{rationale} 3556 The word ``\lstinline$type$'' in a forall specifier is redundant at the moment, but I want to leave 3557 room for inferred parameters of ordinary types in case parameterized types get added one day. 2809 forall( otype T, otype U, otype V ) U * f( T *, U, V * const ); 2810 forall( otype U, otype V, otype W ) U * g( V *, U, W * const ); 2811 \end{lstlisting} 2812 The functions \lstinline$f()$ and \lstinline$g()$ have compatible types. 2813 Let \(f\) and \(g\) be their types; 2814 then \(f_1\) = \lstinline$T$, \(f_2\) = \lstinline$U$, \(f_3\) = \lstinline$V$, \(g_1\) 2815 = \lstinline$V$, \(g_2\) = \lstinline$U$, and \(g_3\) = \lstinline$W$. 2816 Replacing every \(f_i\) by \(g_i\) in \(f\) gives 2817 \begin{lstlisting} 2818 forall( otype V, otype U, otype W ) U * f( V *, U, W * const ); 2819 \end{lstlisting} which has a return type and parameter list that is compatible with \(g\). 2820 \begin{rationale} 2821 The word ``\lstinline$type$'' in a forall specifier is redundant at the moment, but I want to leave room for inferred parameters of ordinary types in case parameterized types get added one day. 3558 2822 3559 2823 Even without parameterized types, I might try to allow 3560 2824 \begin{lstlisting} 3561 2825 forall( int n ) int sum( int vector[n] ); 3562 \end{lstlisting} 3563 but C currently rewrites array parameters as pointer parameters, so the effects of such a change 3564 require more thought. 3565 \end{rationale} 3566 3567 \begin{rationale} 3568 A polymorphic declaration must do two things: it must introduce type parameters, and it must apply 3569 assertions to those types. Adding this to existing C declaration syntax and semantics was delicate, 3570 and not entirely successful. 3571 3572 C depends on declaration-before-use, so a forall specifier must introduce type names before they can 3573 be used in the declaration specifiers. This could be done by making the forall specifier part of 3574 the declaration specifiers, or by making it a new introductory clause of declarations. 3575 3576 Assertions are also part of polymorphic function types, because it must be clear which functions 3577 have access to the assertion parameters declared by the assertions. All attempts to put assertions 3578 inside an introductory clause produced complex semantics and confusing code. Building them into the 3579 declaration specifiers could be done by placing them in the function's parameter list, or in a 3580 forall specifier that is a declaration specifier. Assertions are also used with type parameters of 3581 specifications, and by type declarations. For consistency's sake it seems best to attach assertions 3582 to the type declarations in forall specifiers, which means that forall specifiers must be 3583 declaration specifiers. 2826 \end{lstlisting} but C currently rewrites array parameters as pointer parameters, so the effects of such a change require more thought. 2827 \end{rationale} 2828 2829 \begin{rationale} 2830 A polymorphic declaration must do two things: it must introduce type parameters, and it must apply assertions to those types. 2831 Adding this to existing C declaration syntax and semantics was delicate, and not entirely successful. 2832 2833 C depends on declaration-before-use, so a forall specifier must introduce type names before they can be used in the declaration specifiers. 2834 This could be done by making the forall specifier part of the declaration specifiers, or by making it a new introductory clause of declarations. 2835 2836 Assertions are also part of polymorphic function types, because it must be clear which functions have access to the assertion parameters declared by the assertions. 2837 All attempts to put assertions inside an introductory clause produced complex semantics and confusing code. 2838 Building them into the declaration specifiers could be done by placing them in the function's parameter list, or in a forall specifier that is a declaration specifier. 2839 Assertions are also used with type parameters of specifications, and by type declarations. 2840 For consistency's sake it seems best to attach assertions to the type declarations in forall specifiers, which means that forall specifiers must be declaration specifiers. 3584 2841 \end{rationale} 3585 2842 %HERE … … 3595 2852 3596 2853 \constraints 3597 \lstinline$restrict$\index{register@{\lstinline$restrict$}} Types other than type parameters and 3598 pointer types whose referenced type is an object type shall not be restrict-qualified. 2854 \lstinline$restrict$\index{register@{\lstinline$restrict$}} Types other than type parameters and pointer types whose referenced type is an object type shall not be restrict-qualified. 3599 2855 3600 2856 \semantics 3601 An object's type may be a restrict-qualified type parameter. \lstinline$restrict$ does not 3602 establish any special semantics in that case. 3603 3604 \begin{rationale} 3605 \CFA loosens the constraint on the restrict qualifier so that restrict-qualified pointers may be 3606 passed to polymorphic functions. 3607 \end{rationale} 3608 3609 \lstinline$lvalue$ may be used to qualify the return type of a function type. Let \lstinline$T$ be 3610 an unqualified version of a type; then the result of calling a function with return type 2857 An object's type may be a restrict-qualified type parameter. \lstinline$restrict$ does not establish any special semantics in that case. 2858 2859 \begin{rationale} 2860 \CFA loosens the constraint on the restrict qualifier so that restrict-qualified pointers may be passed to polymorphic functions. 2861 \end{rationale} 2862 2863 \lstinline$lvalue$ may be used to qualify the return type of a function type. 2864 Let \lstinline$T$ be an unqualified version of a type; 2865 then the result of calling a function with return type 3611 2866 \lstinline$lvalue T$ is a \Index{modifiable lvalue} of type \lstinline$T$. 3612 \lstinline$const$\use{const} and \lstinline$volatile$\use{volatile} qualifiers may also be added to 3613 indicate that the function result is a constant or volatile lvalue. 3614 \begin{rationale} 3615 The \lstinline$const$ and \lstinline$volatile$ qualifiers can only be sensibly used to qualify the 3616 return type of a function if the \lstinline$lvalue$ qualifier is also used. 3617 \end{rationale} 3618 3619 An {lvalue}-qualified type may be used in a \Index{cast expression} if the operand is an lvalue; the 3620 result of the expression is an lvalue. 3621 3622 \begin{rationale} 3623 \lstinline$lvalue$ provides some of the functionality of {\CC}'s ``\lstinline$T&$'' ( reference to 3624 object of type \lstinline$T$) type. Reference types have four uses in {\CC}. 2867 \lstinline$const$\use{const} and \lstinline$volatile$\use{volatile} qualifiers may also be added to indicate that the function result is a constant or volatile lvalue. 2868 \begin{rationale} 2869 The \lstinline$const$ and \lstinline$volatile$ qualifiers can only be sensibly used to qualify the return type of a function if the \lstinline$lvalue$ qualifier is also used. 2870 \end{rationale} 2871 2872 An {lvalue}-qualified type may be used in a \Index{cast expression} if the operand is an lvalue; 2873 the result of the expression is an lvalue. 2874 2875 \begin{rationale} 2876 \lstinline$lvalue$ provides some of the functionality of {\CC}'s ``\lstinline$T&$'' ( reference to object of type \lstinline$T$) type. 2877 Reference types have four uses in {\CC}. 3625 2878 \begin{itemize} 3626 2879 \item … … 3629 2882 3630 2883 \item 3631 A reference can be used to define an alias for a complicated lvalue expression, as a way of getting 3632 some of the functionality of the Pascal \lstinline$with$ statement. The following {\CC} code gives 3633 an example. 2884 A reference can be used to define an alias for a complicated lvalue expression, as a way of getting some of the functionality of the Pascal \lstinline$with$ statement. 2885 The following {\CC} code gives an example. 3634 2886 \begin{lstlisting} 3635 2887 { … … 3641 2893 3642 2894 \item 3643 A reference parameter can be used to allow a function to modify an argument without forcing the 3644 caller to pass the address of the argument. This is most useful for user-defined assignment 3645 operators. In {\CC}, plain assignment is done by a function called ``\lstinline$operator=$'', and 3646 the two expressions 2895 A reference parameter can be used to allow a function to modify an argument without forcing the caller to pass the address of the argument. 2896 This is most useful for user-defined assignment operators. 2897 In {\CC}, plain assignment is done by a function called ``\lstinline$operator=$'', and the two expressions 3647 2898 \begin{lstlisting} 3648 2899 a = b; 3649 2900 operator=( a, b ); 3650 \end{lstlisting} 3651 are equivalent. If \lstinline$a$ and \lstinline$b$ are of type \lstinline$T$, then the first 3652 parameter of \lstinline$operator=$ must have type ``\lstinline$T&$''.It cannot have type2901 \end{lstlisting} are equivalent. 2902 If \lstinline$a$ and \lstinline$b$ are of type \lstinline$T$, then the first parameter of \lstinline$operator=$ must have type ``\lstinline$T&$''. 2903 It cannot have type 3653 2904 \lstinline$T$, because then assignment couldn't alter the variable, and it can't have type 3654 2905 ``\lstinline$T *$'', because the assignment would have to be written ``\lstinline$&a = b;$''. 3655 2906 3656 In the case of user-defined operators, this could just as well be handled by using pointer types and 3657 by changing the rewrite rules so that ``\lstinline$a = b;$'' is equivalent to 3658 ``\lstinline$operator=(&( a), b )$''. Reference parameters of ``normal'' functions are Bad Things, 3659 because they remove a useful property of C function calls: an argument can only be modified by a 3660 function if it is preceded by ``\lstinline$&$''. 2907 In the case of user-defined operators, this could just as well be handled by using pointer types and by changing the rewrite rules so that ``\lstinline$a = b;$'' is equivalent to 2908 ``\lstinline$operator=(&( a), b )$''. 2909 Reference parameters of ``normal'' functions are Bad Things, because they remove a useful property of C function calls: an argument can only be modified by a function if it is preceded by ``\lstinline$&$''. 3661 2910 3662 2911 \item … … 3668 2917 void fiddle( const Thing & ); 3669 2918 \end{lstlisting} 3670 If the second form is used, then constructors and destructors are not invoked to create a temporary 3671 variable at the call site ( and it is bad style for the caller to make any assumptions about such 3672 things), and within \lstinline$fiddle$ the parameter is subject to the usual problems caused by 3673 aliases. The reference form might be chosen for efficiency's sake if \lstinline$Thing$s are too 3674 large or their constructors or destructors are too expensive. An implementation may switch between 3675 them without causing trouble for well-behaved clients. This leaves the implementor to define ``too 3676 large'' and ``too expensive''. 2919 If the second form is used, then constructors and destructors are not invoked to create a temporary variable at the call site ( and it is bad style for the caller to make any assumptions about such things), and within \lstinline$fiddle$ the parameter is subject to the usual problems caused by aliases. 2920 The reference form might be chosen for efficiency's sake if \lstinline$Thing$s are too large or their constructors or destructors are too expensive. 2921 An implementation may switch between them without causing trouble for well-behaved clients. 2922 This leaves the implementor to define ``too large'' and ``too expensive''. 3677 2923 3678 2924 I propose to push this job onto the compiler by allowing it to implement 3679 2925 \begin{lstlisting} 3680 2926 void fiddle( const volatile Thing ); 3681 \end{lstlisting} 3682 with call-by-reference. Since it knows all about the size of \lstinline$Thing$s and the parameter 3683 passing mechanism, it should be able to come up with a better definition of ``too large'', and may 3684 be able to make a good guess at ``too expensive''. 2927 \end{lstlisting} with call-by-reference. 2928 Since it knows all about the size of \lstinline$Thing$s and the parameter passing mechanism, it should be able to come up with a better definition of ``too large'', and may be able to make a good guess at ``too expensive''. 3685 2929 \end{itemize} 3686 2930 3687 In summary, since references are only really necessary for returning lvalues, I'll only provide 3688 lvalue functions. 2931 In summary, since references are only really necessary for returning lvalues, I'll only provide lvalue functions. 3689 2932 \end{rationale} 3690 2933 … … 3693 2936 \subsection{Initialization} 3694 2937 3695 An expression that is used as an \nonterm{initializer} is treated as being cast to the type of the 3696 object being initialized. An expression used in an \nonterm{initializer-list} is treated as being 3697 cast to the type of the aggregate member that it initializes. In either case the cast must have a 3698 single unambiguous \Index{interpretation}. 2938 An expression that is used as an \nonterm{initializer} is treated as being cast to the type of the object being initialized. 2939 An expression used in an \nonterm{initializer-list} is treated as being cast to the type of the aggregate member that it initializes. 2940 In either case the cast must have a single unambiguous \Index{interpretation}. 3699 2941 3700 2942 … … 3717 2959 \end{syntax} 3718 2960 \begin{rationale} 3719 The declarations allowed in a specification are much the same as those allowed in a structure, 3720 except that bit fields are not allowed, and \Index{incomplete type}s and function types are allowed. 2961 The declarations allowed in a specification are much the same as those allowed in a structure, except that bit fields are not allowed, and \Index{incomplete type}s and function types are allowed. 3721 2962 \end{rationale} 3722 2963 3723 2964 \semantics 3724 A \define{specification definition} defines a name for a \define{specification}: a parameterized 3725 collection of object and function declarations. 2965 A \define{specification definition} defines a name for a \define{specification}: a parameterized collection of object and function declarations. 3726 2966 3727 2967 The declarations in a specification consist of the declarations in the 3728 2968 \nonterm{spec-declaration-list} and declarations produced by any assertions in the 3729 \nonterm{spec-parameter-list}. If the collection contains two declarations that declare the same 3730 identifier and have compatible types, they are combined into one declaration with the composite type 3731 constructed from the two types. 2969 \nonterm{spec-parameter-list}. 2970 If the collection contains two declarations that declare the same identifier and have compatible types, they are combined into one declaration with the composite type constructed from the two types. 3732 2971 3733 2972 … … 3747 2986 3748 2987 \constraints 3749 The \nonterm{identifier} in an assertion that is not a \nonterm{spec-declaration} shall be the name 3750 of a specification. The \nonterm{type-name-list} shall contain one \nonterm{type-name} argument for 3751 each \nonterm{type-parameter} in that specification's \nonterm{spec-parameter-list}. If the 3752 \nonterm{type-parameter} uses type-class \lstinline$type$\use{type}, the argument shall be the type 3753 name of an \Index{object type}; if it uses \lstinline$dtype$, the argument shall be the type name of 3754 an object type or an \Index{incomplete type}; and if it uses \lstinline$ftype$, the argument shall 3755 be the type name of a \Index{function type}. 2988 The \nonterm{identifier} in an assertion that is not a \nonterm{spec-declaration} shall be the name of a specification. 2989 The \nonterm{type-name-list} shall contain one \nonterm{type-name} argument for each \nonterm{type-parameter} in that specification's \nonterm{spec-parameter-list}. 2990 If the 2991 \nonterm{type-parameter} uses type-class \lstinline$type$\use{type}, the argument shall be the type name of an \Index{object type}; 2992 if it uses \lstinline$dtype$, the argument shall be the type name of an object type or an \Index{incomplete type}; 2993 and if it uses \lstinline$ftype$, the argument shall be the type name of a \Index{function type}. 3756 2994 3757 2995 \semantics … … 3759 2997 \define{assertion parameters}. 3760 2998 3761 The assertion parameters produced by an assertion that applies the name of a specification to type 3762 arguments are found by taking the declarations specified in the specification and treating each of 3763 the specification's parameters as a synonym for the corresponding \nonterm{type-name} argument. 3764 3765 The collection of assertion parameters produced by the \nonterm{assertion-list} are found by 3766 combining the declarations produced by each assertion. If the collection contains two declarations 3767 that declare the same identifier and have compatible types, they are combined into one declaration 3768 with the \Index{composite type} constructed from the two types. 2999 The assertion parameters produced by an assertion that applies the name of a specification to type arguments are found by taking the declarations specified in the specification and treating each of the specification's parameters as a synonym for the corresponding \nonterm{type-name} argument. 3000 3001 The collection of assertion parameters produced by the \nonterm{assertion-list} are found by combining the declarations produced by each assertion. 3002 If the collection contains two declarations that declare the same identifier and have compatible types, they are combined into one declaration with the \Index{composite type} constructed from the two types. 3769 3003 3770 3004 \examples 3771 3005 \begin{lstlisting} 3772 forall( type T | T ?*?( T, T ))@\use{?*?}@3006 forall( otype T | T ?*?( T, T ))@\use{?*?}@ 3773 3007 T square( T val ) {@\impl{square}@ 3774 3008 return val + val; 3775 3009 } 3776 3777 context summable( type T ) {@\impl{summable}@ 3010 trait summable( otype T ) {@\impl{summable}@ 3778 3011 T ?+=?( T *, T );@\use{?+=?}@ 3779 3012 const T 0;@\use{0}@ 3780 3013 }; 3781 context list_of( type List,type Element ) {@\impl{list_of}@3014 trait list_of( otype List, otype Element ) {@\impl{list_of}@ 3782 3015 Element car( List ); 3783 3016 List cdr( List ); … … 3786 3019 int is_nil( List ); 3787 3020 }; 3788 context sum_list( type List, type Element | summable( Element ) | list_of( List, Element ) ) {}; 3789 \end{lstlisting} 3790 \lstinline$sum_list$ contains seven declarations, which describe a list whose elements can be added 3791 up. The assertion ``\lstinline$|sum_list( i_list, int )$''\use{sum_list} produces the assertion 3792 parameters 3021 trait sum_list( otype List, otype Element | summable( Element ) | list_of( List, Element ) ) {}; 3022 \end{lstlisting} 3023 \lstinline$sum_list$ contains seven declarations, which describe a list whose elements can be added up. 3024 The assertion ``\lstinline$|sum_list( i_list, int )$''\use{sum_list} produces the assertion parameters 3793 3025 \begin{lstlisting} 3794 3026 int ?+=?( int *, int ); … … 3825 3057 3826 3058 \constraints 3827 If a type declaration has block scope, and the declared identifier has external or internal linkage, 3828 the declaration shall have no initializer for the identifier. 3059 If a type declaration has block scope, and the declared identifier has external or internal linkage, the declaration shall have no initializer for the identifier. 3829 3060 3830 3061 \semantics 3831 A \nonterm{type-parameter} or a \nonterm{type-declarator} declares an identifier to be a \Index{type 3832 name} for a type incompatible with all other types. 3833 3834 An identifier declared by a \nonterm{type-parameter} has \Index{no linkage}. Identifiers declared 3835 with type-class \lstinline$type$\use{type} are \Index{object type}s; those declared with type-class 3836 \lstinline$dtype$\use{dtype} are \Index{incomplete type}s; and those declared with type-class 3837 \lstinline$ftype$\use{ftype} are \Index{function type}s. The identifier has \Index{block scope} that 3838 terminates at the end of the \nonterm{spec-declaration-list} or polymorphic function that contains 3839 the \nonterm{type-parameter}. 3840 3841 A \nonterm{type-declarator} with an \Index{initializer} is a \define{type definition}. The declared 3842 identifier is an \Index{incomplete type} within the initializer, and an \Index{object type} after 3843 the end of the initializer. The type in the initializer is called the \define{implementation 3844 type}. Within the scope of the declaration, \Index{implicit conversion}s can be performed between 3845 the defined type and the implementation type, and between pointers to the defined type and pointers 3846 to the implementation type. 3847 3848 A type declaration without an \Index{initializer} and without a \Index{storage-class specifier} or 3849 with storage-class specifier \lstinline$static$\use{static} defines an \Index{incomplete type}. If a 3850 \Index{translation unit} or \Index{block} contains one or more such declarations for an identifier, 3851 it must contain exactly one definition of the identifier ( but not in an enclosed block, which would 3852 define a new type known only within that block). 3062 A \nonterm{type-parameter} or a \nonterm{type-declarator} declares an identifier to be a \Index{type name} for a type incompatible with all other types. 3063 3064 An identifier declared by a \nonterm{type-parameter} has \Index{no linkage}. 3065 Identifiers declared with type-class \lstinline$type$\use{type} are \Index{object type}s; 3066 those declared with type-class 3067 \lstinline$dtype$\use{dtype} are \Index{incomplete type}s; 3068 and those declared with type-class 3069 \lstinline$ftype$\use{ftype} are \Index{function type}s. 3070 The identifier has \Index{block scope} that terminates at the end of the \nonterm{spec-declaration-list} or polymorphic function that contains the \nonterm{type-parameter}. 3071 3072 A \nonterm{type-declarator} with an \Index{initializer} is a \define{type definition}. The declared identifier is an \Index{incomplete type} within the initializer, and an \Index{object type} after the end of the initializer. 3073 The type in the initializer is called the \define{implementation 3074 type}. 3075 Within the scope of the declaration, \Index{implicit conversion}s can be performed between the defined type and the implementation type, and between pointers to the defined type and pointers to the implementation type. 3076 3077 A type declaration without an \Index{initializer} and without a \Index{storage-class specifier} or with storage-class specifier \lstinline$static$\use{static} defines an \Index{incomplete type}. 3078 If a 3079 \Index{translation unit} or \Index{block} contains one or more such declarations for an identifier, it must contain exactly one definition of the identifier ( but not in an enclosed block, which would define a new type known only within that block). 3853 3080 \begin{rationale} 3854 3081 Incomplete type declarations allow compact mutually-recursive types. 3855 3082 \begin{lstlisting} 3856 type t1; // Incomplete type declaration. 3857 type t2 = struct { t1 * p; ... }; 3858 type t1 = struct { t2 * p; ... }; 3859 \end{lstlisting} 3860 Without them, mutual recursion could be handled by declaring mutually recursive structures, then 3861 initializing the types to those structures. 3083 otype t1; // incomplete type declaration 3084 otype t2 = struct { t1 * p; ... }; 3085 otype t1 = struct { t2 * p; ... }; 3086 \end{lstlisting} 3087 Without them, mutual recursion could be handled by declaring mutually recursive structures, then initializing the types to those structures. 3862 3088 \begin{lstlisting} 3863 3089 struct s1; 3864 type t2 = struct s2 { struct s1 * p; ... }; 3865 type t1 = struct s1 { struct s2 * p; ... }; 3866 \end{lstlisting} 3867 This introduces extra names, and may force the programmer to cast between the types and their 3868 implementations. 3090 otype t2 = struct s2 { struct s1 * p; ... }; 3091 otype t1 = struct s1 { struct s2 * p; ... }; 3092 \end{lstlisting} 3093 This introduces extra names, and may force the programmer to cast between the types and their implementations. 3869 3094 \end{rationale} 3870 3095 3871 3096 A type declaration without an initializer and with \Index{storage-class specifier} 3872 \lstinline$extern$\use{extern} is an \define{opaque type declaration}. Opaque types are3873 \Index{object type}s. An opaque type is not a \nonterm{constant-expression}; neither is a structure3874 or union that has a member whose type is not a \nonterm{constant-expression}. Every other 3875 \Index{object type} is a \nonterm{constant-expression}. Objects with static storage duration shall 3876 be declared with a type that is a \nonterm{constant-expression}. 3877 \ begin{rationale}3878 Type declarations can declare identifiers with external linkage, whereas typedef declarations 3879 declare identifiers that only exist within a translation unit. These opaque types can be used in 3880 declarations, but the implementation of the type is not visible.3881 3882 Static objects can not have opaque types because space for them would have to be allocated at 3883 program start-up. This is a deficiency\index{deficiencies!static opaque objects}, but I don't want 3884 to deal with ``module initialization'' code just now.3885 \end{rationale} 3886 3887 An \Index{incomplete type} which is not a qualified version\index{qualified type} of a type is a 3888 value of \Index{type-class} \lstinline$dtype$. An object type\index{object types} which is not a 3889 qualified version of a type is a value of type-classes \lstinline$type$ and \lstinline$dtype$.A3097 \lstinline$extern$\use{extern} is an \define{opaque type declaration}. 3098 Opaque types are 3099 \Index{object type}s. 3100 An opaque type is not a \nonterm{constant-expression}; 3101 neither is a structure or union that has a member whose type is not a \nonterm{constant-expression}. Every other 3102 \Index{object type} is a \nonterm{constant-expression}. 3103 Objects with static storage duration shall be declared with a type that is a \nonterm{constant-expression}. 3104 \begin{rationale} 3105 Type declarations can declare identifiers with external linkage, whereas typedef declarations declare identifiers that only exist within a translation unit. 3106 These opaque types can be used in declarations, but the implementation of the type is not visible. 3107 3108 Static objects can not have opaque types because space for them would have to be allocated at program start-up. 3109 This is a deficiency\index{deficiencies!static opaque objects}, but I don't want to deal with ``module initialization'' code just now. 3110 \end{rationale} 3111 3112 An \Index{incomplete type} which is not a qualified version\index{qualified type} of a type is a value of \Index{type-class} \lstinline$dtype$. 3113 An object type\index{object types} which is not a qualified version of a type is a value of type-classes \lstinline$type$ and \lstinline$dtype$. 3114 A 3890 3115 \Index{function type} is a value of type-class \lstinline$ftype$. 3891 3116 \begin{rationale} 3892 Syntactically, a type value is a \nonterm{type-name}, which is a declaration for an object which 3893 omits the identifier being declared. 3894 3895 Object types are precisely the types that can be instantiated. Type qualifiers are not included in 3896 type values because the compiler needs the information they provide at compile time to detect 3897 illegal statements or to produce efficient machine instructions. For instance, the code that a 3898 compiler must generate to manipulate an object that has volatile-qualified type may be different 3899 from the code to manipulate an ordinary object. 3900 3901 Type qualifiers are a weak point of C's type system. Consider the standard library function 3902 \lstinline$strchr()$ which, given a string and a character, returns a pointer to the first 3903 occurrence of the character in the string. 3117 Syntactically, a type value is a \nonterm{type-name}, which is a declaration for an object which omits the identifier being declared. 3118 3119 Object types are precisely the types that can be instantiated. 3120 Type qualifiers are not included in type values because the compiler needs the information they provide at compile time to detect illegal statements or to produce efficient machine instructions. 3121 For instance, the code that a compiler must generate to manipulate an object that has volatile-qualified type may be different from the code to manipulate an ordinary object. 3122 3123 Type qualifiers are a weak point of C's type system. 3124 Consider the standard library function 3125 \lstinline$strchr()$ which, given a string and a character, returns a pointer to the first occurrence of the character in the string. 3904 3126 \begin{lstlisting} 3905 3127 char *strchr( const char *s, int c ) {@\impl{strchr}@ 3906 3128 char real_c = c; // done because c was declared as int. 3907 3129 for ( ; *s != real_c; s++ ) 3908 if ( *s == '\0' ) return NULL;3130 if ( *s == '\0' ) return NULL; 3909 3131 return ( char * )s; 3910 3132 } 3911 3133 \end{lstlisting} 3912 The parameter \lstinline$s$ must be \lstinline$const char *$, because \lstinline$strchr()$ might be 3913 used to search a constant string, but the return type must be \lstinline$char *$, because the result 3914 might be used to modify a non-constant string. Hence the body must perform a cast, and ( even worse) 3915 \lstinline$strchr()$ provides a type-safe way to attempt to modify constant strings. What is needed 3916 is some way to say that \lstinline$s$'s type might contain qualifiers, and the result type has 3917 exactly the same qualifiers. Polymorphic functions do not provide a fix for this 3918 deficiency\index{deficiencies!pointers to qualified types}, because type qualifiers are not part of 3919 type values. Instead, overloading can be used to define \lstinline$strchr()$ for each combination 3920 of qualifiers. 3921 \end{rationale} 3922 3923 \begin{rationale} 3924 Since \Index{incomplete type}s are not type values, they can not be used as the initializer in a 3925 type declaration, or as the type of a structure or union member. This prevents the declaration of 3926 types that contain each other. 3927 \begin{lstlisting} 3928 type t1; 3929 type t2 = t1; // illegal: incomplete type t1. 3930 type t1 = t2; 3931 \end{lstlisting} 3932 3933 The initializer in a file-scope declaration must be a constant expression. This means type 3934 declarations can not build on opaque types, which is a deficiency\index{deficiencies!nesting opaque 3134 The parameter \lstinline$s$ must be \lstinline$const char *$, because \lstinline$strchr()$ might be used to search a constant string, but the return type must be \lstinline$char *$, because the result might be used to modify a non-constant string. 3135 Hence the body must perform a cast, and ( even worse) 3136 \lstinline$strchr()$ provides a type-safe way to attempt to modify constant strings. 3137 What is needed is some way to say that \lstinline$s$'s type might contain qualifiers, and the result type has exactly the same qualifiers. 3138 Polymorphic functions do not provide a fix for this deficiency\index{deficiencies!pointers to qualified types}, because type qualifiers are not part of type values. 3139 Instead, overloading can be used to define \lstinline$strchr()$ for each combination of qualifiers. 3140 \end{rationale} 3141 3142 \begin{rationale} 3143 Since \Index{incomplete type}s are not type values, they can not be used as the initializer in a type declaration, or as the type of a structure or union member. 3144 This prevents the declaration of types that contain each other. 3145 \begin{lstlisting} 3146 otype t1; 3147 otype t2 = t1; // illegal: incomplete type t1 3148 otype t1 = t2; 3149 \end{lstlisting} 3150 3151 The initializer in a file-scope declaration must be a constant expression. 3152 This means type declarations can not build on opaque types, which is a deficiency\index{deficiencies!nesting opaque 3935 3153 types}. 3936 3154 \begin{lstlisting} 3937 extern type Huge; // extended-precision integer type.3938 type Rational = struct {3155 extern otype Huge; // extended-precision integer type 3156 otype Rational = struct { 3939 3157 Huge numerator, denominator; // illegal 3940 3158 }; … … 3944 3162 \end{lstlisting} 3945 3163 Without this restriction, \CFA might require ``module initialization'' code ( since 3946 \lstinline$Rational$ has external linkage, it must be created before any other translation unit 3947 instantiates it), and would force an ordering on the initialization of the translation unit that 3948 defines \lstinline$Huge$ and the translation that declares \lstinline$Rational$. 3949 3950 A benefit of the restriction is that it prevents the declaration in separate translation units of 3951 types that contain each other, which would be hard to prevent otherwise. 3164 \lstinline$Rational$ has external linkage, it must be created before any other translation unit instantiates it), and would force an ordering on the initialization of the translation unit that defines \lstinline$Huge$ and the translation that declares \lstinline$Rational$. 3165 3166 A benefit of the restriction is that it prevents the declaration in separate translation units of types that contain each other, which would be hard to prevent otherwise. 3952 3167 \begin{lstlisting} 3953 3168 // File a.c: … … 3962 3177 \begin{rationale} 3963 3178 Since a \nonterm{type-declaration} is a \nonterm{declaration} and not a 3964 \nonterm{struct-declaration}, type declarations can not be structure members. The form of 3179 \nonterm{struct-declaration}, type declarations can not be structure members. 3180 The form of 3965 3181 \nonterm{type-declaration} forbids arrays of, pointers to, and functions returning \lstinline$type$. 3966 Hence the syntax of \nonterm{type-specifier} does not have to be extended to allow type-valued 3967 expressions. It also side-steps the problem of type-valued expressions producing different values 3968 in different declarations. 3969 3970 Since a type declaration is not a \nonterm{parameter-declaration}, functions can not have explicit 3971 type parameters. This may be too restrictive, but it attempts to make compilation simpler. Recall 3972 that when traditional C scanners read in an identifier, they look it up in the symbol table to 3973 determine whether or not it is a typedef name, and return a ``type'' or ``identifier'' token 3974 depending on what they find. A type parameter would add a type name to the current scope. The 3975 scope manipulations involved in parsing the declaration of a function that takes function pointer 3976 parameters and returns a function pointer may just be too complicated. 3977 3978 Explicit type parameters don't seem to be very useful, anyway, because their scope would not include 3979 the return type of the function. Consider the following attempt to define a type-safe memory 3980 allocation function. 3182 Hence the syntax of \nonterm{type-specifier} does not have to be extended to allow type-valued expressions. 3183 It also side-steps the problem of type-valued expressions producing different values in different declarations. 3184 3185 Since a type declaration is not a \nonterm{parameter-declaration}, functions can not have explicit type parameters. 3186 This may be too restrictive, but it attempts to make compilation simpler. 3187 Recall that when traditional C scanners read in an identifier, they look it up in the symbol table to determine whether or not it is a typedef name, and return a ``type'' or ``identifier'' token depending on what they find. 3188 A type parameter would add a type name to the current scope. 3189 The scope manipulations involved in parsing the declaration of a function that takes function pointer parameters and returns a function pointer may just be too complicated. 3190 3191 Explicit type parameters don't seem to be very useful, anyway, because their scope would not include the return type of the function. 3192 Consider the following attempt to define a type-safe memory allocation function. 3981 3193 \begin{lstlisting} 3982 3194 #include <stdlib.h> 3983 T * new( type T ) { return ( T * )malloc( sizeof( T) ); }; 3984 @\ldots@ 3985 int * ip = new( int ); 3986 \end{lstlisting} 3987 This looks sensible, but \CFA's declaration-before-use rules mean that ``\lstinline$T$'' in the 3988 function body refers to the parameter, but the ``\lstinline$T$'' in the return type refers to the 3989 meaning of \lstinline$T$ in the scope that contains \lstinline$new$; it could be undefined, or a 3990 type name, or a function or variable name. Nothing good can result from such a situation. 3195 T * new( otype T ) { return ( T * )malloc( sizeof( T) ); }; 3196 @\ldots@ int * ip = new( int ); 3197 \end{lstlisting} 3198 This looks sensible, but \CFA's declaration-before-use rules mean that ``\lstinline$T$'' in the function body refers to the parameter, but the ``\lstinline$T$'' in the return type refers to the meaning of \lstinline$T$ in the scope that contains \lstinline$new$; 3199 it could be undefined, or a type name, or a function or variable name. 3200 Nothing good can result from such a situation. 3991 3201 \end{rationale} 3992 3202 … … 3994 3204 Since type declarations create new types, instances of types are always passed by value. 3995 3205 \begin{lstlisting} 3996 type A1 = int[2];3206 otype A1 = int[2]; 3997 3207 void f1( A1 a ) { a[0] = 0; }; 3998 typedef int A2[2];3208 otypedef int A2[2]; 3999 3209 void f2( A2 a ) { a[0] = 0; }; 4000 3210 A1 v1; … … 4003 3213 f2( v2 ); 4004 3214 \end{lstlisting} 4005 \lstinline$V1$ is passed by value, so \lstinline$f1()$'s assignment to \lstinline$a[0]$ does not 4006 modify v1. \lstinline$V2$ is converted to a pointer, so \lstinline$f2()$ modifies 4007 \lstinline$v2[0]$. 3215 \lstinline$V1$ is passed by value, so \lstinline$f1()$'s assignment to \lstinline$a[0]$ does not modify v1. \lstinline$V2$ is converted to a pointer, so \lstinline$f2()$ modifies \lstinline$v2[0]$. 4008 3216 4009 3217 A translation unit containing the declarations 4010 3218 \begin{lstlisting} 4011 extern type Complex;@\use{Complex}@ // opaque type declaration .3219 extern type Complex;@\use{Complex}@ // opaque type declaration 4012 3220 extern float abs( Complex );@\use{abs}@ 4013 \end{lstlisting} 4014 can contain declarations of complex numbers, which can be passed to \lstinline$abs$. Some other 4015 translation unit must implement \lstinline$Complex$ and \lstinline$abs$. That unit might contain 4016 the declarations 4017 \begin{lstlisting} 4018 type Complex = struct { float re, im; };@\impl{Complex}@ 3221 \end{lstlisting} can contain declarations of complex numbers, which can be passed to \lstinline$abs$. 3222 Some other translation unit must implement \lstinline$Complex$ and \lstinline$abs$. 3223 That unit might contain the declarations 3224 \begin{lstlisting} 3225 otype Complex = struct { float re, im; };@\impl{Complex}@ 4019 3226 Complex cplx_i = { 0.0, 1.0 };@\impl{cplx_i}@ 4020 3227 float abs( Complex c ) {@\impl{abs( Complex )}@ … … 4022 3229 } 4023 3230 \end{lstlisting} 4024 Note that \lstinline$c$ is implicitly converted to a \lstinline$struct$ so that its components can 4025 be retrieved. 4026 4027 \begin{lstlisting} 4028 type Time_of_day = int;@\impl{Time_of_day}@ // seconds since midnight. 3231 Note that \lstinline$c$ is implicitly converted to a \lstinline$struct$ so that its components can be retrieved. 3232 3233 \begin{lstlisting} 3234 otype Time_of_day = int;@\impl{Time_of_day}@ // seconds since midnight. 4029 3235 Time_of_day ?+?( Time_of_day t1, int seconds ) {@\impl{?+?}@ 4030 3236 return (( int)t1 + seconds ) % 86400; … … 4034 3240 4035 3241 \begin{rationale} 4036 Within the scope of a type definition, an instance of the type can be viewed as having that type or 4037 as having the implementation type. In the \lstinline$Time_of_day$ example, the difference is 4038 important. Different languages have treated the distinction between the abstraction and the 4039 implementation in different ways. 3242 Within the scope of a type definition, an instance of the type can be viewed as having that type or as having the implementation type. 3243 In the \lstinline$Time_of_day$ example, the difference is important. 3244 Different languages have treated the distinction between the abstraction and the implementation in different ways. 4040 3245 \begin{itemize} 4041 3246 \item 4042 Inside a Clu cluster \cite{clu}, the declaration of an instance states which view applies. Two 4043 primitives called \lstinline$up$ and \lstinline$down$ can be used to convert between the views. 4044 \item 4045 The Simula class \cite{Simula87} is essentially a record type. Since the only operations on a 4046 record are member selection and assignment, which can not be overloaded, there is never any 4047 ambiguity as to whether the abstraction or the implementation view is being used. In {\CC} 4048 \cite{c++}, operations on class instances include assignment and ``\lstinline$&$'', which can be 4049 overloaded. A ``scope resolution'' operator can be used inside the class to specify whether the 4050 abstract or implementation version of the operation should be used. 4051 \item 4052 An Ada derived type definition \cite{ada} creates a new type from an old type, and also implicitly 4053 declares derived subprograms that correspond to the existing subprograms that use the old type as a 4054 parameter type or result type. The derived subprograms are clones of the existing subprograms with 4055 the old type replaced by the derived type. Literals and aggregates of the old type are also cloned. 3247 Inside a Clu cluster \cite{CLU}, the declaration of an instance states which view applies. 3248 Two primitives called \lstinline$up$ and \lstinline$down$ can be used to convert between the views. 3249 \item 3250 The Simula class \cite{SIMULA87} is essentially a record type. 3251 Since the only operations on a record are member selection and assignment, which can not be overloaded, there is never any ambiguity as to whether the abstraction or the implementation view is being used. 3252 In {\CC} 3253 \cite{C++}, operations on class instances include assignment and ``\lstinline$&$'', which can be overloaded. 3254 A ``scope resolution'' operator can be used inside the class to specify whether the abstract or implementation version of the operation should be used. 3255 \item 3256 An Ada derived type definition \cite{Ada} creates a new type from an old type, and also implicitly declares derived subprograms that correspond to the existing subprograms that use the old type as a parameter type or result type. 3257 The derived subprograms are clones of the existing subprograms with the old type replaced by the derived type. 3258 Literals and aggregates of the old type are also cloned. 4056 3259 In other words, the abstract view provides exactly the same operations as the implementation view. 4057 3260 This allows the abstract view to be used in all cases. 4058 3261 4059 The derived subprograms can be replaced by programmer-specified subprograms. This is an exception4060 to the normal scope rules, which forbid duplicate definitions of a subprogram in a scope. In this 4061 case, explicit conversions between the derived type and the old type can be used.3262 The derived subprograms can be replaced by programmer-specified subprograms. 3263 This is an exception to the normal scope rules, which forbid duplicate definitions of a subprogram in a scope. 3264 In this case, explicit conversions between the derived type and the old type can be used. 4062 3265 \end{itemize} 4063 \CFA's rules are like Clu's, except that implicit conversions and 4064 conversion costs allow it to do away with most uses of \lstinline$up$ and \lstinline$down$. 3266 \CFA's rules are like Clu's, except that implicit conversions and conversion costs allow it to do away with most uses of \lstinline$up$ and \lstinline$down$. 4065 3267 \end{rationale} 4066 3268 … … 4070 3272 A declaration\index{type declaration} of a type identifier \lstinline$T$ with type-class 4071 3273 \lstinline$type$ implicitly declares a \define{default assignment} function 4072 \lstinline$T ?=?( T *, T )$\use{?=?}, with the same \Index{scope} and \Index{linkage} as the 4073 identifier \lstinline$T$. 4074 \begin{rationale} 4075 Assignment is central to C's imperative programming style, and every existing C object type has 4076 assignment defined for it ( except for array types, which are treated as pointer types for purposes 4077 of assignment). Without this rule, nearly every inferred type parameter would need an accompanying 4078 assignment assertion parameter. If a type parameter should not have an assignment operation, 4079 \lstinline$dtype$ should be used. If a type should not have assignment defined, the user can define 4080 an assignment function that causes a run-time error, or provide an external declaration but no 4081 definition and thus cause a link-time error. 4082 \end{rationale} 4083 4084 A definition\index{type definition} of a type identifier \lstinline$T$ with \Index{implementation 4085 type} \lstinline$I$ and type-class \lstinline$type$ implicitly defines a default assignment 4086 function. A definition\index{type definition} of a type identifier \lstinline$T$ with implementation 4087 type \lstinline$I$ and an assertion list implicitly defines \define{default function}s and 4088 \define{default object}s as declared by the assertion declarations. The default objects and 4089 functions have the same \Index{scope} and \Index{linkage} as the identifier \lstinline$T$. Their 4090 values are determined as follows: 3274 \lstinline$T ?=?( T *, T )$\use{?=?}, with the same \Index{scope} and \Index{linkage} as the identifier \lstinline$T$. 3275 \begin{rationale} 3276 Assignment is central to C's imperative programming style, and every existing C object type has assignment defined for it ( except for array types, which are treated as pointer types for purposes of assignment). 3277 Without this rule, nearly every inferred type parameter would need an accompanying assignment assertion parameter. 3278 If a type parameter should not have an assignment operation, 3279 \lstinline$dtype$ should be used. 3280 If a type should not have assignment defined, the user can define an assignment function that causes a run-time error, or provide an external declaration but no definition and thus cause a link-time error. 3281 \end{rationale} 3282 3283 A definition\index{type definition} of a type identifier \lstinline$T$ with \Index{implementation type} \lstinline$I$ and type-class \lstinline$type$ implicitly defines a default assignment function. 3284 A definition\index{type definition} of a type identifier \lstinline$T$ with implementation type \lstinline$I$ and an assertion list implicitly defines \define{default function}s and 3285 \define{default object}s as declared by the assertion declarations. 3286 The default objects and functions have the same \Index{scope} and \Index{linkage} as the identifier \lstinline$T$. 3287 Their values are determined as follows: 4091 3288 \begin{itemize} 4092 3289 \item 4093 If at the definition of \lstinline$T$ there is visible a declaration of an object with the same name 4094 as the default object, and if the type of that object with all occurrence of \lstinline$I$ replaced 4095 by \lstinline$T$ is compatible with the type of the default object, then the default object is 4096 initialized with that object. Otherwise the scope of the declaration of \lstinline$T$ must contain 4097 a definition of the default object. 3290 If at the definition of \lstinline$T$ there is visible a declaration of an object with the same name as the default object, and if the type of that object with all occurrence of \lstinline$I$ replaced by \lstinline$T$ is compatible with the type of the default object, then the default object is initialized with that object. 3291 Otherwise the scope of the declaration of \lstinline$T$ must contain a definition of the default object. 4098 3292 4099 3293 \item 4100 If at the definition of \lstinline$T$ there is visible a declaration of a function with the same 4101 name as the default function, and if the type of that function with all occurrence of \lstinline$I$ 4102 replaced by \lstinline$T$ is compatible with the type of the default function, then the default 4103 function calls that function after converting its arguments and returns the converted result. 4104 4105 Otherwise, if \lstinline$I$ contains exactly one anonymous member\index{anonymous member} such that 4106 at the definition of \lstinline$T$ there is visible a declaration of a function with the same name 4107 as the default function, and the type of that function with all occurrences of the anonymous 4108 member's type in its parameter list replaced by \lstinline$T$ is compatible with the type of the 4109 default function, then the default function calls that function after converting its arguments and 4110 returns the result. 4111 4112 Otherwise the scope of the declaration of \lstinline$T$ must contain a definition of the default 4113 function. 3294 If at the definition of \lstinline$T$ there is visible a declaration of a function with the same name as the default function, and if the type of that function with all occurrence of \lstinline$I$ replaced by \lstinline$T$ is compatible with the type of the default function, then the default function calls that function after converting its arguments and returns the converted result. 3295 3296 Otherwise, if \lstinline$I$ contains exactly one anonymous member\index{anonymous member} such that at the definition of \lstinline$T$ there is visible a declaration of a function with the same name as the default function, and the type of that function with all occurrences of the anonymous member's type in its parameter list replaced by \lstinline$T$ is compatible with the type of the default function, then the default function calls that function after converting its arguments and returns the result. 3297 3298 Otherwise the scope of the declaration of \lstinline$T$ must contain a definition of the default function. 4114 3299 \end{itemize} 4115 3300 \begin{rationale} 4116 Note that a pointer to a default function will not compare as equal to a pointer to the inherited 4117 function. 4118 \end{rationale} 4119 4120 A function or object with the same type and name as a default function or object that is declared 4121 within the scope of the definition of \lstinline$T$ replaces the default function or object. 3301 Note that a pointer to a default function will not compare as equal to a pointer to the inherited function. 3302 \end{rationale} 3303 3304 A function or object with the same type and name as a default function or object that is declared within the scope of the definition of \lstinline$T$ replaces the default function or object. 4122 3305 4123 3306 \examples 4124 3307 \begin{lstlisting} 4125 context s(type T ) {3308 trait s( otype T ) { 4126 3309 T a, b; 4127 } 4128 struct impl { int left, right; } a = { 0, 0 }; 4129 type Pair | s( Pair ) = struct impl; 3310 } struct impl { int left, right; } a = { 0, 0 }; 3311 otype Pair | s( Pair ) = struct impl; 4130 3312 Pair b = { 1, 1 }; 4131 3313 \end{lstlisting} 4132 3314 The definition of \lstinline$Pair$ implicitly defines two objects \lstinline$a$ and \lstinline$b$. 4133 \lstinline$Pair a$ inherits its value from the \lstinline$struct impl a$. The definition of4134 \lstinline$Pair b$ is compulsory because there is no \lstinline$struct impl b$ to construct a value 4135 from.4136 \begin{lstlisting} 4137 context ss(type T ) {3315 \lstinline$Pair a$ inherits its value from the \lstinline$struct impl a$. 3316 The definition of 3317 \lstinline$Pair b$ is compulsory because there is no \lstinline$struct impl b$ to construct a value from. 3318 \begin{lstlisting} 3319 trait ss( otype T ) { 4138 3320 T clone( T ); 4139 3321 void munge( T * ); 4140 3322 } 4141 type Whatsit | ss( Whatsit );@\use{Whatsit}@4142 type Doodad | ss( Doodad ) = struct doodad {@\use{Doodad}@3323 otype Whatsit | ss( Whatsit );@\use{Whatsit}@ 3324 otype Doodad | ss( Doodad ) = struct doodad {@\use{Doodad}@ 4143 3325 Whatsit; // anonymous member 4144 3326 int extra; … … 4152 3334 void munge( Doodad * ); 4153 3335 \end{lstlisting} 4154 The assignment function inherits \lstinline$struct doodad$'s assignment function because the types 4155 match when \lstinline$struct doodad$ is replaced by \lstinline$Doodad$ throughout. 3336 The assignment function inherits \lstinline$struct doodad$'s assignment function because the types match when \lstinline$struct doodad$ is replaced by \lstinline$Doodad$ throughout. 4156 3337 \lstinline$munge()$ inherits \lstinline$Whatsit$'s \lstinline$munge()$ because the types match when 4157 \lstinline$Whatsit$ is replaced by \lstinline$Doodad$ in the parameter list. \lstinline$clone()$ 4158 does \emph{not} inherit \lstinline$Whatsit$'s \lstinline$clone()$: replacement in the parameter 4159 list yields ``\lstinline$Whatsit clone( Doodad )$'', which is not compatible with 4160 \lstinline$Doodad$'s \lstinline$clone()$'s type. Hence the definition of 3338 \lstinline$Whatsit$ is replaced by \lstinline$Doodad$ in the parameter list. \lstinline$clone()$ does \emph{not} inherit \lstinline$Whatsit$'s \lstinline$clone()$: replacement in the parameter list yields ``\lstinline$Whatsit clone( Doodad )$'', which is not compatible with 3339 \lstinline$Doodad$'s \lstinline$clone()$'s type. 3340 Hence the definition of 4161 3341 ``\lstinline$Doodad clone( Doodad )$'' is necessary. 4162 3342 4163 3343 Default functions and objects are subject to the normal scope rules. 4164 3344 \begin{lstlisting} 4165 type T = @\ldots@;3345 otype T = @\ldots@; 4166 3346 T a_T = @\ldots@; // Default assignment used. 4167 3347 T ?=?( T *, T ); … … 4173 3353 4174 3354 \begin{rationale} 4175 The \emph{class} construct of object-oriented programming languages performs three independent 4176 functions. It \emph{encapsulates} a data structure; it defines a \emph{subtype} relationship, whereby 4177 i nstances of one class may be used in contexts that require instances of another; and it allows one4178 class to \emph{inherit} the implementation of another.4179 4180 In \CFA, encapsulation is provided by opaque types and the scope rules, and subtyping is provided 4181 by specifications and assertions.Inheritance is provided by default functions and objects.3355 The \emph{class} construct of object-oriented programming languages performs three independent functions. 3356 It \emph{encapsulates} a data structure; 3357 it defines a \emph{subtype} relationship, whereby instances of one class may be used in contexts that require instances of another; 3358 and it allows one class to \emph{inherit} the implementation of another. 3359 3360 In \CFA, encapsulation is provided by opaque types and the scope rules, and subtyping is provided by specifications and assertions. 3361 Inheritance is provided by default functions and objects. 4182 3362 \end{rationale} 4183 3363 … … 4190 3370 \end{syntax} 4191 3371 4192 Many statements contain expressions, which may have more than one interpretation. The following4193 sections describe how the \CFA translator selects an interpretation. In all cases the result of the 4194 selection shall be a single unambiguous \Index{interpretation}.3372 Many statements contain expressions, which may have more than one interpretation. 3373 The following sections describe how the \CFA translator selects an interpretation. 3374 In all cases the result of the selection shall be a single unambiguous \Index{interpretation}. 4195 3375 4196 3376 … … 4239 3419 switch ( E ) ... 4240 3420 choose ( E ) ... 4241 \end{lstlisting} 4242 may have more than one interpretation, but it shall have only one interpretation with an integral type. 3421 \end{lstlisting} may have more than one interpretation, but it shall have only one interpretation with an integral type. 4243 3422 An \Index{integer promotion} is performed on the expression if necessary. 4244 3423 The constant expressions in \lstinline$case$ statements with the switch are converted to the promoted type. … … 4284 3463 while ( E ) ... 4285 3464 do ... while ( E ); 4286 \end{lstlisting} 4287 is treated as ``\lstinline$( int )((E)!=0)$''. 3465 \end{lstlisting} is treated as ``\lstinline$( int )((E)!=0)$''. 4288 3466 4289 3467 The statement 4290 3468 \begin{lstlisting} 4291 3469 for ( a; b; c ) @\ldots@ 4292 \end{lstlisting} 4293 is treated as 3470 \end{lstlisting} is treated as 4294 3471 \begin{lstlisting} 4295 3472 for ( ( void )( a ); ( int )(( b )!=0); ( void )( c ) ) ... … … 4413 3590 4414 3591 The implementation shall define the macro names \lstinline$__LINE__$, \lstinline$__FILE__$, 4415 \lstinline$__DATE__$, and \lstinline$__TIME__$, as in the {\c11} standard. It shall not define the 4416 macro name \lstinline$__STDC__$. 4417 4418 In addition, the implementation shall define the macro name \lstinline$__CFORALL__$ to be the 4419 decimal constant 1. 3592 \lstinline$__DATE__$, and \lstinline$__TIME__$, as in the {\c11} standard. 3593 It shall not define the macro name \lstinline$__STDC__$. 3594 3595 In addition, the implementation shall define the macro name \lstinline$__CFORALL__$ to be the decimal constant 1. 4420 3596 4421 3597 … … 4427 3603 4428 3604 \section{C types} 4429 This section gives example specifications for some groups of types that are important in the C 4430 language, in terms of the predefined operations that can be applied to those types. 3605 This section gives example specifications for some groups of types that are important in the C language, in terms of the predefined operations that can be applied to those types. 4431 3606 4432 3607 4433 3608 \subsection{Scalar, arithmetic, and integral types} 4434 3609 4435 The pointer, integral, and floating-point types are all \define{scalar types}. All of these types4436 can be logically negated and compared. The assertion ``\lstinline$scalar( Complex )$'' should be read 4437 as ``type \lstinline$Complex$ is scalar''.4438 \begin{lstlisting} 4439 context scalar(type T ) {@\impl{scalar}@3610 The pointer, integral, and floating-point types are all \define{scalar types}. 3611 All of these types can be logically negated and compared. 3612 The assertion ``\lstinline$scalar( Complex )$'' should be read as ``type \lstinline$Complex$ is scalar''. 3613 \begin{lstlisting} 3614 trait scalar( otype T ) {@\impl{scalar}@ 4440 3615 int !?( T ); 4441 3616 int ?<?( T, T ), ?<=?( T, T ), ?==?( T, T ), ?>=?( T, T ), ?>?( T, T ), ?!=?( T, T ); … … 4443 3618 \end{lstlisting} 4444 3619 4445 The integral and floating-point types are \define{arithmetic types}, which support the basic 4446 arithmetic operators. The use of an assertion in the \nonterm{spec-parameter-list} declares that, 4447 in order to be arithmetic, a type must also be scalar ( and hence that scalar operations are 4448 available ). This is equivalent to inheritance of specifications. 4449 \begin{lstlisting} 4450 context arithmetic( type T | scalar( T ) ) {@\impl{arithmetic}@@\use{scalar}@ 3620 The integral and floating-point types are \define{arithmetic types}, which support the basic arithmetic operators. 3621 The use of an assertion in the \nonterm{spec-parameter-list} declares that, in order to be arithmetic, a type must also be scalar ( and hence that scalar operations are available ). 3622 This is equivalent to inheritance of specifications. 3623 \begin{lstlisting} 3624 trait arithmetic( otype T | scalar( T ) ) {@\impl{arithmetic}@@\use{scalar}@ 4451 3625 T +?( T ), -?( T ); 4452 3626 T ?*?( T, T ), ?/?( T, T ), ?+?( T, T ), ?-?( T, T ); … … 4457 3631 \define{integral types}. 4458 3632 \begin{lstlisting} 4459 context integral(type T | arithmetic( T ) ) {@\impl{integral}@@\use{arithmetic}@3633 trait integral( otype T | arithmetic( T ) ) {@\impl{integral}@@\use{arithmetic}@ 4460 3634 T ~?( T ); 4461 3635 T ?&?( T, T ), ?|?( T, T ), ?^?( T, T ); … … 4471 3645 The only operation that can be applied to all modifiable lvalues is simple assignment. 4472 3646 \begin{lstlisting} 4473 context m_lvalue(type T ) {@\impl{m_lvalue}@3647 trait m_lvalue( otype T ) {@\impl{m_lvalue}@ 4474 3648 T ?=?( T *, T ); 4475 3649 }; … … 4477 3651 4478 3652 Modifiable scalar lvalues are scalars and are modifiable lvalues, and assertions in the 4479 \nonterm{spec-parameter-list} reflect those relationships. This is equivalent to multiple 4480 inheritance of specifications. Scalars can also be incremented and decremented. 4481 \begin{lstlisting} 4482 context m_l_scalar( type T | scalar( T ) | m_lvalue( T ) ) {@\impl{m_l_scalar}@ 3653 \nonterm{spec-parameter-list} reflect those relationships. 3654 This is equivalent to multiple inheritance of specifications. 3655 Scalars can also be incremented and decremented. 3656 \begin{lstlisting} 3657 trait m_l_scalar( otype T | scalar( T ) | m_lvalue( T ) ) {@\impl{m_l_scalar}@ 4483 3658 T ?++( T * ), ?--( T * );@\use{scalar}@@\use{m_lvalue}@ 4484 3659 T ++?( T * ), --?( T * ); … … 4486 3661 \end{lstlisting} 4487 3662 4488 Modifiable arithmetic lvalues are both modifiable scalar lvalues and arithmetic. Note that this4489 results in the ``inheritance'' of \lstinline$scalar$ along both paths.4490 \begin{lstlisting} 4491 context m_l_arithmetic(type T | m_l_scalar( T ) | arithmetic( T ) ) {@\impl{m_l_arithmetic}@3663 Modifiable arithmetic lvalues are both modifiable scalar lvalues and arithmetic. 3664 Note that this results in the ``inheritance'' of \lstinline$scalar$ along both paths. 3665 \begin{lstlisting} 3666 trait m_l_arithmetic( otype T | m_l_scalar( T ) | arithmetic( T ) ) {@\impl{m_l_arithmetic}@ 4492 3667 T ?/=?( T *, T ), ?*=?( T *, T );@\use{m_l_scalar}@@\use{arithmetic}@ 4493 3668 T ?+=?( T *, T ), ?-=?( T *, T ); 4494 3669 }; 4495 4496 context m_l_integral( type T | m_l_arithmetic( T ) | integral( T ) ) {@\impl{m_l_integral}@ 3670 trait m_l_integral( otype T | m_l_arithmetic( T ) | integral( T ) ) {@\impl{m_l_integral}@ 4497 3671 T ?&=?( T *, T ), ?|=?( T *, T ), ?^=?( T *, T );@\use{m_l_arithmetic}@ 4498 3672 T ?%=?( T *, T ), ?<<=?( T *, T ), ?>>=?( T *, T );@\use{integral}@ … … 4503 3677 \subsection{Pointer and array types} 4504 3678 4505 Array types can barely be said to exist in {\c11}, since in most cases an array name is treated as a 4506 constant pointer to the first element of the array, and the subscript expression 3679 Array types can barely be said to exist in {\c11}, since in most cases an array name is treated as a constant pointer to the first element of the array, and the subscript expression 4507 3680 ``\lstinline$a[i]$'' is equivalent to the dereferencing expression ``\lstinline$(*( a+( i )))$''. 4508 3681 Technically, pointer arithmetic and pointer comparisons other than ``\lstinline$==$'' and 4509 ``\lstinline$!=$'' are only defined for pointers to array elements, but the type system does not 4510 enforce those restrictions. Consequently, there is no need for a separate ``array type'' 4511 specification. 4512 4513 Pointer types are scalar types.Like other scalar types, they have ``\lstinline$+$'' and3682 ``\lstinline$!=$'' are only defined for pointers to array elements, but the type system does not enforce those restrictions. 3683 Consequently, there is no need for a separate ``array type'' specification. 3684 3685 Pointer types are scalar types. 3686 Like other scalar types, they have ``\lstinline$+$'' and 4514 3687 ``\lstinline$-$'' operators, but the types do not match the types of the operations in 4515 3688 \lstinline$arithmetic$, so these operators cannot be consolidated in \lstinline$scalar$. 4516 3689 \begin{lstlisting} 4517 context pointer( type P | scalar( P ) ) {@\impl{pointer}@@\use{scalar}@3690 trait pointer( type P | scalar( P ) ) {@\impl{pointer}@@\use{scalar}@ 4518 3691 P ?+?( P, long int ), ?+?( long int, P ), ?-?( P, long int ); 4519 3692 ptrdiff_t ?-?( P, P ); 4520 3693 }; 4521 4522 context m_l_pointer( type P | pointer( P ) | m_l_scalar( P ) ) {@\impl{m_l_pointer}@ 3694 trait m_l_pointer( type P | pointer( P ) | m_l_scalar( P ) ) {@\impl{m_l_pointer}@ 4523 3695 P ?+=?( P *, long int ), ?-=?( P *, long int ); 4524 3696 P ?=?( P *, void * ); … … 4527 3699 \end{lstlisting} 4528 3700 4529 Specifications that define the dereference operator ( or subscript operator ) require two 4530 parameters, one for the pointer type and one for the pointed-at ( or element ) type. Different 4531 specifications are needed for each set of \Index{type qualifier}s, because qualifiers are not 4532 included in types. The assertion ``\lstinline$|ptr_to( Safe_pointer, int )$'' should be read as 3701 Specifications that define the dereference operator ( or subscript operator ) require two parameters, one for the pointer type and one for the pointed-at ( or element ) type. 3702 Different specifications are needed for each set of \Index{type qualifier}s, because qualifiers are not included in types. 3703 The assertion ``\lstinline$|ptr_to( Safe_pointer, int )$'' should be read as 4533 3704 ``\lstinline$Safe_pointer$ acts like a pointer to \lstinline$int$''. 4534 3705 \begin{lstlisting} 4535 context ptr_to( type P | pointer( P ), type T ) {@\impl{ptr_to}@@\use{pointer}@ 4536 lvalue T *?( P ); lvalue T ?[?]( P, long int ); 3706 trait ptr_to( otype P | pointer( P ), otype T ) {@\impl{ptr_to}@@\use{pointer}@ 3707 lvalue T *?( P ); 3708 lvalue T ?[?]( P, long int ); 4537 3709 }; 4538 4539 context ptr_to_const( type P | pointer( P ), type T ) {@\impl{ptr_to_const}@ 4540 const lvalue T *?( P ); const lvalue T?[?]( P, long int );@\use{pointer}@3710 trait ptr_to_const( otype P | pointer( P ), otype T ) {@\impl{ptr_to_const}@ 3711 const lvalue T *?( P ); 3712 const lvalue T ?[?]( P, long int );@\use{pointer}@ 4541 3713 }; 4542 4543 context ptr_to_volatile( type P | pointer( P ), type T ) }@\impl{ptr_to_volatile}@ 4544 volatile lvalue T *?( P ); volatile lvalue T?[?]( P, long int );@\use{pointer}@3714 trait ptr_to_volatile( otype P | pointer( P ), otype T ) }@\impl{ptr_to_volatile}@ 3715 volatile lvalue T *?( P ); 3716 volatile lvalue T ?[?]( P, long int );@\use{pointer}@ 4545 3717 }; 4546 \end{lstlisting} 4547 \begin{lstlisting} 4548 context ptr_to_const_volatile( type P | pointer( P ), type T ) }@\impl{ptr_to_const_volatile}@ 3718 trait ptr_to_const_volatile( otype P | pointer( P ), otype T ) }@\impl{ptr_to_const_volatile}@ 4549 3719 const volatile lvalue T *?( P );@\use{pointer}@ 4550 3720 const volatile lvalue T ?[?]( P, long int ); … … 4552 3722 \end{lstlisting} 4553 3723 4554 Assignment to pointers is more complicated than is the case with other types, because the target's 4555 type can have extra type qualifiers in the pointed-at type: a ``\lstinline$T *$'' can be assigned to 4556 a ``\lstinline$const T *$'', a ``\lstinline$volatile T *$'', and a ``\lstinline$const volatile T *$''. 3724 Assignment to pointers is more complicated than is the case with other types, because the target's type can have extra type qualifiers in the pointed-at type: a ``\lstinline$T *$'' can be assigned to a ``\lstinline$const T *$'', a ``\lstinline$volatile T *$'', and a ``\lstinline$const volatile T *$''. 4557 3725 Again, the pointed-at type is passed in, so that assertions can connect these specifications to the 4558 3726 ``\lstinline$ptr_to$'' specifications. 4559 3727 \begin{lstlisting} 4560 context m_l_ptr_to( type P | m_l_pointer( P ),@\use{m_l_pointer}@@\impl{m_l_ptr_to}@type T | ptr_to( P, T )@\use{ptr_to}@ {3728 trait m_l_ptr_to( otype P | m_l_pointer( P ),@\use{m_l_pointer}@@\impl{m_l_ptr_to}@ otype T | ptr_to( P, T )@\use{ptr_to}@ { 4561 3729 P ?=?( P *, T * ); 4562 3730 T * ?=?( T **, P ); 4563 3731 }; 4564 4565 context m_l_ptr_to_const( type P | m_l_pointer( P ),@\use{m_l_pointer}@@\impl{m_l_ptr_to_const}@ type T | ptr_to_const( P, T )@\use{ptr_to_const}@) { 3732 trait m_l_ptr_to_const( otype P | m_l_pointer( P ),@\use{m_l_pointer}@@\impl{m_l_ptr_to_const}@ otype T | ptr_to_const( P, T )@\use{ptr_to_const}@) { 4566 3733 P ?=?( P *, const T * ); 4567 3734 const T * ?=?( const T **, P ); 4568 3735 }; 4569 4570 context m_l_ptr_to_volatile( type P | m_l_pointer( P ),@\use{m_l_pointer}@@\impl{m_l_ptr_to_volatile}@ type T | ptr_to_volatile( P, T )) {@\use{ptr_to_volatile}@ 3736 trait m_l_ptr_to_volatile( otype P | m_l_pointer( P ),@\use{m_l_pointer}@@\impl{m_l_ptr_to_volatile}@ otype T | ptr_to_volatile( P, T )) {@\use{ptr_to_volatile}@ 4571 3737 P ?=?( P *, volatile T * ); 4572 3738 volatile T * ?=?( volatile T **, P ); 4573 3739 }; 4574 4575 context m_l_ptr_to_const_volatile( type P | ptr_to_const_volatile( P ),@\use{ptr_to_const_volatile}@@\impl{m_l_ptr_to_const_volatile}@ 4576 type T | m_l_ptr_to_volatile( P, T ) | m_l_ptr_to_const( P )) {@\use{m_l_ptr_to_const}@@\use{m_l_ptr_to_volatile}@ 3740 trait m_l_ptr_to_const_volatile( otype P | ptr_to_const_volatile( P ),@\use{ptr_to_const_volatile}@@\impl{m_l_ptr_to_const_volatile}@ 3741 otype T | m_l_ptr_to_volatile( P, T ) | m_l_ptr_to_const( P )) {@\use{m_l_ptr_to_const}@@\use{m_l_ptr_to_volatile}@ 4577 3742 P ?=?( P *, const volatile T * ); 4578 3743 const volatile T * ?=?( const volatile T **, P ); … … 4580 3745 \end{lstlisting} 4581 3746 4582 Note the regular manner in which type qualifiers appear in those specifications. An alternative 4583 specification can make use of the fact that qualification of the pointed-at type is part of a 4584 pointer type to capture that regularity. 4585 \begin{lstlisting} 4586 context m_l_ptr_like( type MyP | m_l_pointer( MyP ),@\use{m_l_pointer}@@\impl{m_l_ptr_like}@ type CP | m_l_pointer( CP ) ) { 3747 Note the regular manner in which type qualifiers appear in those specifications. 3748 An alternative specification can make use of the fact that qualification of the pointed-at type is part of a pointer type to capture that regularity. 3749 \begin{lstlisting} 3750 trait m_l_ptr_like( type MyP | m_l_pointer( MyP ),@\use{m_l_pointer}@@\impl{m_l_ptr_like}@ type CP | m_l_pointer( CP ) ) { 4587 3751 MyP ?=?( MyP *, CP ); 4588 3752 CP ?=?( CP *, MyP ); … … 4590 3754 \end{lstlisting} 4591 3755 The assertion ``\lstinline$| m_l_ptr_like( Safe_ptr, const int * )$'' should be read as 4592 ``\lstinline$Safe_ptr$ is a pointer type like \lstinline$const int *$''. This specification has two4593 defects, compared to the original four: there is no automatic assertion that dereferencing a3756 ``\lstinline$Safe_ptr$ is a pointer type like \lstinline$const int *$''. 3757 This specification has two defects, compared to the original four: there is no automatic assertion that dereferencing a 4594 3758 \lstinline$MyP$ produces an lvalue of the type that \lstinline$CP$ points at, and the 4595 ``\lstinline$|m_l_pointer( CP )$'' assertion provides only a weak assurance that the argument passed 4596 to \lstinline$CP$ really is a pointer type. 3759 ``\lstinline$|m_l_pointer( CP )$'' assertion provides only a weak assurance that the argument passed to \lstinline$CP$ really is a pointer type. 4597 3760 4598 3761 4599 3762 \section{Relationships between operations} 4600 3763 4601 Different operators often have related meanings; for instance, in C, ``\lstinline$+$'', 3764 Different operators often have related meanings; 3765 for instance, in C, ``\lstinline$+$'', 4602 3766 ``\lstinline$+=$'', and the two versions of ``\lstinline$++$'' perform variations of addition. 4603 Languages like {\CC} and Ada allow programmers to define operators for new types, but do not 4604 require that these relationships be preserved, or even that all of the operators be implemented. 4605 Completeness and consistency is left to the good taste and discretion of the programmer. It is 4606 possible to encourage these attributes by providing generic operator functions, or member functions 4607 of abstract classes, that are defined in terms of other, related operators. 4608 4609 In \CFA, polymorphic functions provide the equivalent of these generic operators, and 4610 specifications explicitly define the minimal implementation that a programmer should provide. This 4611 section shows a few examples. 3767 Languages like {\CC} and Ada allow programmers to define operators for new types, but do not require that these relationships be preserved, or even that all of the operators be implemented. 3768 Completeness and consistency is left to the good taste and discretion of the programmer. 3769 It is possible to encourage these attributes by providing generic operator functions, or member functions of abstract classes, that are defined in terms of other, related operators. 3770 3771 In \CFA, polymorphic functions provide the equivalent of these generic operators, and specifications explicitly define the minimal implementation that a programmer should provide. 3772 This section shows a few examples. 4612 3773 4613 3774 4614 3775 \subsection{Relational and equality operators} 4615 3776 4616 The different comparison operators have obvious relationships, but there is no obvious subset of the 4617 operations to use in the implementation of the others. However, it is usually convenient to 4618 implement a single comparison function that returns a negative integer, 0, or a positive integer if 4619 its first argument is respectively less than, equal to, or greater than its second argument; the 4620 library function \lstinline$strcmp$ is an example. 4621 4622 C and \CFA have an extra, non-obvious comparison operator: ``\lstinline$!$'', logical negation, 4623 returns 1 if its operand compares equal to 0, and 0 otherwise. 4624 \begin{lstlisting} 4625 context comparable( type T ) { 3777 The different comparison operators have obvious relationships, but there is no obvious subset of the operations to use in the implementation of the others. 3778 However, it is usually convenient to implement a single comparison function that returns a negative integer, 0, or a positive integer if its first argument is respectively less than, equal to, or greater than its second argument; 3779 the library function \lstinline$strcmp$ is an example. 3780 3781 C and \CFA have an extra, non-obvious comparison operator: ``\lstinline$!$'', logical negation, returns 1 if its operand compares equal to 0, and 0 otherwise. 3782 \begin{lstlisting} 3783 trait comparable( otype T ) { 4626 3784 const T 0; 4627 3785 int compare( T, T ); 4628 3786 } 4629 4630 forall( type T | comparable( T ) ) int ?<?( T l, T r ) { 3787 forall( otype T | comparable( T ) ) int ?<?( T l, T r ) { 4631 3788 return compare( l, r ) < 0; 4632 3789 } 4633 3790 // ... similarly for <=, ==, >=, >, and !=. 4634 4635 forall( type T | comparable( T ) ) int !?( T operand ) { 3791 forall( otype T | comparable( T ) ) int !?( T operand ) { 4636 3792 return !compare( operand, 0 ); 4637 3793 } … … 4641 3797 \subsection{Arithmetic and integer operations} 4642 3798 4643 A complete arithmetic type would provide the arithmetic operators and the corresponding assignment 4644 operators. Of these, the assignment operators are more likely to be implemented directly, because 4645 it is usually more efficient to alter the contents of an existing object than to create and return a 4646 new one. Similarly, a complete integral type would provide integral operations based on integral 4647 assignment operations. 4648 \begin{lstlisting} 4649 context arith_base( type T ) { 3799 A complete arithmetic type would provide the arithmetic operators and the corresponding assignment operators. 3800 Of these, the assignment operators are more likely to be implemented directly, because it is usually more efficient to alter the contents of an existing object than to create and return a new one. 3801 Similarly, a complete integral type would provide integral operations based on integral assignment operations. 3802 \begin{lstlisting} 3803 trait arith_base( otype T ) { 4650 3804 const T 1; 4651 3805 T ?+=?( T *, T ), ?-=?( T *, T ), ?*=?( T *, T ), ?/=?( T *, T ); 4652 3806 } 4653 4654 forall( type T | arith_base( T ) ) T ?+?( T l, T r ) { 3807 forall( otype T | arith_base( T ) ) T ?+?( T l, T r ) { 4655 3808 return l += r; 4656 3809 } 4657 4658 forall( type T | arith_base( T ) ) T ?++( T * operand ) { 3810 forall( otype T | arith_base( T ) ) T ?++( T * operand ) { 4659 3811 T temporary = *operand; 4660 3812 *operand += 1; 4661 3813 return temporary; 4662 3814 } 4663 4664 forall( type T | arith_base( T ) ) T ++?( T * operand ) { 3815 forall( otype T | arith_base( T ) ) T ++?( T * operand ) { 4665 3816 return *operand += 1; 4666 3817 } 4667 3818 // ... similarly for -, --, *, and /. 4668 4669 context int_base( type T ) { 3819 trait int_base( otype T ) { 4670 3820 T ?&=?( T *, T ), ?|=?( T *, T ), ?^=?( T *, T ); 4671 3821 T ?%=?( T *, T ), ?<<=?( T *, T ), ?>>=?( T *, T ); 4672 3822 } 4673 4674 forall( type T | int_base( T ) ) T ?&?( T l, T r ) { 3823 forall( otype T | int_base( T ) ) T ?&?( T l, T r ) { 4675 3824 return l &= r; 4676 3825 } … … 4678 3827 \end{lstlisting} 4679 3828 4680 Note that, although an arithmetic type would certainly provide comparison functions, and an integral 4681 type would provide arithmetic operations, there does not have to be any relationship among 4682 \lstinline$int_base$, \lstinline$arith_base$ and \lstinline$comparable$. Note also that these 4683 declarations provide guidance and assistance, but they do not define an absolutely minimal set of 4684 requirements. A truly minimal implementation of an arithmetic type might only provide 3829 Note that, although an arithmetic type would certainly provide comparison functions, and an integral type would provide arithmetic operations, there does not have to be any relationship among 3830 \lstinline$int_base$, \lstinline$arith_base$ and \lstinline$comparable$. 3831 Note also that these declarations provide guidance and assistance, but they do not define an absolutely minimal set of requirements. 3832 A truly minimal implementation of an arithmetic type might only provide 4685 3833 \lstinline$0$, \lstinline$1$, and \lstinline$?-=?$, which would be used by polymorphic 4686 3834 \lstinline$?+=?$, \lstinline$?*=?$, and \lstinline$?/=?$ functions. … … 4692 3840 Review index entries. 4693 3841 4694 Restrict allowed to qualify anything, or type/dtype parameters, but only affects pointers. This gets 4695 into \lstinline$noalias$ territory. Qualifying anything (``\lstinline$short restrict rs$'') means 4696 pointer parameters of \lstinline$?++$, etc, would need restrict qualifiers. 4697 4698 Enumerated types. Constants are not ints. Overloading. Definition should be ``representable as an 4699 integer type'', not ``as an int''. C11 usual conversions freely convert to and from ordinary 4700 integer types via assignment, which works between any integer types. Does enum Color ?*?( enum 3842 Restrict allowed to qualify anything, or type/dtype parameters, but only affects pointers. 3843 This gets into \lstinline$noalias$ territory. 3844 Qualifying anything (``\lstinline$short restrict rs$'') means pointer parameters of \lstinline$?++$, etc, would need restrict qualifiers. 3845 3846 Enumerated types. 3847 Constants are not ints. 3848 Overloading. 3849 Definition should be ``representable as an integer type'', not ``as an int''. 3850 C11 usual conversions freely convert to and from ordinary integer types via assignment, which works between any integer types. 3851 Does enum Color ?*?( enum 4701 3852 Color, enum Color ) really make sense? ?++ does, but it adds (int)1. 4702 3853 4703 Operators on {,signed,unsigned} char and other small types. ?<? harmless; ?*? questionable for 4704 chars. Generic selections make these choices visible. Safe conversion operators? Predefined 3854 Operators on {,signed,unsigned} char and other small types. ?<? harmless; 3855 ?*? questionable for chars. 3856 Generic selections make these choices visible. 3857 Safe conversion operators? Predefined 4705 3858 ``promotion'' function? 4706 3859 4707 \lstinline$register$ assignment might be handled as assignment to a temporary with copying back and 4708 forth, but copying must not be done by assignment. 3860 \lstinline$register$ assignment might be handled as assignment to a temporary with copying back and forth, but copying must not be done by assignment. 4709 3861 4710 3862 Don't use ptrdiff\_t by name in the predefineds. 4711 3863 4712 Polymorphic objects. Polymorphic typedefs and type declarations. 3864 Polymorphic objects. 3865 Polymorphic typedefs and type declarations. 4713 3866 4714 3867 4715 3868 \bibliographystyle{plain} 4716 \bibliography{ refrat}3869 \bibliography{cfa} 4717 3870 4718 3871 4719 3872 \addcontentsline{toc}{chapter}{\indexname} % add index name to table of contents 4720 3873 \begin{theindex} 4721 Italic page numbers give the location of the main entry for the referenced term. Plain page numbers 4722 denote uses of the indexed term. Entries for grammar non-terminals are italicized. A typewriter 4723 font is used for grammar terminals and program identifiers. 3874 Italic page numbers give the location of the main entry for the referenced term. 3875 Plain page numbers denote uses of the indexed term. 3876 Entries for grammar non-terminals are italicized. 3877 A typewriter font is used for grammar terminals and program identifiers. 4724 3878 \indexspace 4725 3879 \input{refrat.ind}
Note:
See TracChangeset
for help on using the changeset viewer.