Changeset 92f8e18 for doc


Ignore:
Timestamp:
Feb 9, 2018, 4:30:17 PM (6 years ago)
Author:
Aaron Moss <a3moss@…>
Branches:
ADT, aaron-thesis, arm-eh, ast-experimental, cleanup-dtors, deferred_resn, demangler, enum, forall-pointer-decay, jacob/cs343-translation, jenkins-sandbox, master, new-ast, new-ast-unique-expr, new-env, no_list, persistent-indexer, pthread-emulation, qualifiedEnum, resolv-new, with_gc
Children:
826a67c
Parents:
119bb6a (diff), a722c7a (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.
Message:

Merge branch 'master' of plg.uwaterloo.ca:software/cfa/cfa-cc

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1 edited

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  • doc/papers/general/Paper.tex

    r119bb6a r92f8e18  
    102102\makeatother
    103103
     104\newenvironment{cquote}{%
     105        \list{}{\lstset{resetmargins=true,aboveskip=0pt,belowskip=0pt}\topsep=4pt\parsep=0pt\leftmargin=\parindent\rightmargin\leftmargin}%
     106        \item\relax
     107}{%
     108        \endlist
     109}% cquote
     110
    104111% CFA programming language, based on ANSI C (with some gcc additions)
    105112\lstdefinelanguage{CFA}[ANSI]{C}{
    … …  
    227234int forty_two = identity( 42 );                         $\C{// T is bound to int, forty\_two == 42}$
    228235\end{lstlisting}
    229 The @identity@ function above can be applied to any complete \emph{object type} (or @otype@).
     236The @identity@ function above can be applied to any complete \newterm{object type} (or @otype@).
    230237The type variable @T@ is transformed into a set of additional implicit parameters encoding sufficient information about @T@ to create and return a variable of that type.
    231238The \CFA implementation passes the size and alignment of the type represented by an @otype@ parameter, as well as an assignment operator, constructor, copy constructor and destructor.
    232 If this extra information is not needed, \eg for a pointer, the type parameter can be declared as a \emph{data type} (or @dtype@).
     239If this extra information is not needed, \eg for a pointer, the type parameter can be declared as a \newterm{data type} (or @dtype@).
    233240
    234241In \CFA, the polymorphism runtime-cost is spread over each polymorphic call, due to passing more arguments to polymorphic functions;
    … …  
    236243A design advantage is that, unlike \CC template-functions, \CFA polymorphic-functions are compatible with C \emph{separate compilation}, preventing compilation and code bloat.
    237244
    238 Since bare polymorphic-types provide a restricted set of available operations, \CFA provides a \emph{type assertion}~\cite[pp.~37-44]{Alphard} mechanism to provide further type information, where type assertions may be variable or function declarations that depend on a polymorphic type-variable.
     245Since bare polymorphic-types provide a restricted set of available operations, \CFA provides a \newterm{type assertion}~\cite[pp.~37-44]{Alphard} mechanism to provide further type information, where type assertions may be variable or function declarations that depend on a polymorphic type-variable.
    239246For example, the function @twice@ can be defined using the \CFA syntax for operator overloading:
    240247\begin{lstlisting}
    … …  
    306313\subsection{Traits}
    307314
    308 \CFA provides \emph{traits} to name a group of type assertions, where the trait name allows specifying the same set of assertions in multiple locations, preventing repetition mistakes at each function declaration:
     315\CFA provides \newterm{traits} to name a group of type assertions, where the trait name allows specifying the same set of assertions in multiple locations, preventing repetition mistakes at each function declaration:
    309316\begin{lstlisting}
    310317trait summable( otype T ) {
    … …  
    330337Given the information provided for an @otype@, variables of polymorphic type can be treated as if they were a complete type: stack-allocatable, default or copy-initialized, assigned, and deleted.
    331338
    332 In summation, the \CFA type-system uses \emph{nominal typing} for concrete types, matching with the C type-system, and \emph{structural typing} for polymorphic types.
     339In summation, the \CFA type-system uses \newterm{nominal typing} for concrete types, matching with the C type-system, and \newterm{structural typing} for polymorphic types.
    333340Hence, trait names play no part in type equivalence;
    334341the names are simply macros for a list of polymorphic assertions, which are expanded at usage sites.
    … …  
    375382Furthermore, writing and using preprocessor macros can be unnatural and inflexible.
    376383
    377 \CC, Java, and other languages use \emph{generic types} to produce type-safe abstract data-types.
     384\CC, Java, and other languages use \newterm{generic types} to produce type-safe abstract data-types.
    378385\CFA also implements generic types that integrate efficiently and naturally with the existing polymorphic functions, while retaining backwards compatibility with C and providing separate compilation.
    379386However, for known concrete parameters, the generic-type definition can be inlined, like \CC templates.
    … …  
    396403\end{lstlisting}
    397404
    398 \CFA classifies generic types as either \emph{concrete} or \emph{dynamic}.
     405\CFA classifies generic types as either \newterm{concrete} or \newterm{dynamic}.
    399406Concrete types have a fixed memory layout regardless of type parameters, while dynamic types vary in memory layout depending on their type parameters.
    400 A type may have polymorphic parameters but still be concrete, called \emph{dtype-static}.
     407A type may have polymorphic parameters but still be concrete, called \newterm{dtype-static}.
    401408Polymorphic pointers are an example of dtype-static types, \eg @forall(dtype T) T *@ is a polymorphic type, but for any @T@, @T *@  is a fixed-sized pointer, and therefore, can be represented by a @void *@ in code generation.
    402409
    … …  
    435442Though \CFA implements concrete generic-types efficiently, it also has a fully general system for dynamic generic types.
    436443As mentioned in Section~\ref{sec:poly-fns}, @otype@ function parameters (in fact all @sized@ polymorphic parameters) come with implicit size and alignment parameters provided by the caller.
    437 Dynamic generic-types also have an \emph{offset array} containing structure-member offsets.
     444Dynamic generic-types also have an \newterm{offset array} containing structure-member offsets.
    438445A dynamic generic-union needs no such offset array, as all members are at offset 0, but size and alignment are still necessary.
    439446Access to members of a dynamic structure is provided at runtime via base-displacement addressing with the structure pointer and the member offset (similar to the @offsetof@ macro), moving a compile-time offset calculation to runtime.
    … …  
    448455For instance, modularity is generally provided in C by including an opaque forward-declaration of a structure and associated accessor and mutator functions in a header file, with the actual implementations in a separately-compiled @.c@ file.
    449456\CFA supports this pattern for generic types, but the caller does not know the actual layout or size of the dynamic generic-type, and only holds it by a pointer.
    450 The \CFA translator automatically generates \emph{layout functions} for cases where the size, alignment, and offset array of a generic struct cannot be passed into a function from that function's caller.
     457The \CFA translator automatically generates \newterm{layout functions} for cases where the size, alignment, and offset array of a generic struct cannot be passed into a function from that function's caller.
    451458These layout functions take as arguments pointers to size and alignment variables and a caller-allocated array of member offsets, as well as the size and alignment of all @sized@ parameters to the generic structure (un@sized@ parameters are forbidden from being used in a context that affects layout).
    452459Results of these layout functions are cached so that they are only computed once per type per function. %, as in the example below for @pair@.
    … …  
    472479Since @pair(T *, T * )@ is a concrete type, there are no implicit parameters passed to @lexcmp@, so the generated code is identical to a function written in standard C using @void *@, yet the \CFA version is type-checked to ensure the fields of both pairs and the arguments to the comparison function match in type.
    473480
    474 Another useful pattern enabled by reused dtype-static type instantiations is zero-cost \emph{tag-structures}.
     481Another useful pattern enabled by reused dtype-static type instantiations is zero-cost \newterm{tag-structures}.
    475482Sometimes information is only used for type-checking and can be omitted at runtime, \eg:
    476483\begin{lstlisting}
    … …  
    528535The addition of multiple-return-value functions (MRVF) are useless without a syntax for accepting multiple values at the call-site.
    529536The simplest mechanism for capturing the return values is variable assignment, allowing the values to be retrieved directly.
    530 As such, \CFA allows assigning multiple values from a function into multiple variables, using a square-bracketed list of lvalue expressions (as above), called a \emph{tuple}.
    531 
    532 However, functions also use \emph{composition} (nested calls), with the direct consequence that MRVFs must also support composition to be orthogonal with single-returning-value functions (SRVF), \eg:
     537As such, \CFA allows assigning multiple values from a function into multiple variables, using a square-bracketed list of lvalue expressions (as above), called a \newterm{tuple}.
     538
     539However, functions also use \newterm{composition} (nested calls), with the direct consequence that MRVFs must also support composition to be orthogonal with single-returning-value functions (SRVF), \eg:
    533540\begin{lstlisting}
    534541printf( "%d %d\n", div( 13, 5 ) );                      $\C{// return values seperated into arguments}$
    … …  
    563570printf( "%d %d\n", qr );
    564571\end{lstlisting}
    565 \CFA also supports \emph{tuple indexing} to access single components of a tuple expression:
     572\CFA also supports \newterm{tuple indexing} to access single components of a tuple expression:
    566573\begin{lstlisting}
    567574[int, int] * p = &qr;                                           $\C{// tuple pointer}$
    … …  
    606613\subsection{Tuple Assignment}
    607614
    608 An assignment where the left side is a tuple type is called \emph{tuple assignment}.
    609 There are two kinds of tuple assignment depending on whether the right side of the assignment operator has a tuple type or a non-tuple type, called \emph{multiple} and \emph{mass assignment}, respectively.
     615An assignment where the left side is a tuple type is called \newterm{tuple assignment}.
     616There are two kinds of tuple assignment depending on whether the right side of the assignment operator has a tuple type or a non-tuple type, called \newterm{multiple} and \newterm{mass assignment}, respectively.
    610617%\lstDeleteShortInline@%
    611618%\par\smallskip
    … …  
    641648\subsection{Member Access}
    642649
    643 It is also possible to access multiple fields from a single expression using a \emph{member-access}.
     650It is also possible to access multiple fields from a single expression using a \newterm{member-access}.
    644651The result is a single tuple-valued expression whose type is the tuple of the types of the members, \eg:
    645652\begin{lstlisting}
    … …  
    771778Matching against a @ttype@ parameter consumes all remaining argument components and packages them into a tuple, binding to the resulting tuple of types.
    772779In a given parameter list, there must be at most one @ttype@ parameter that occurs last, which matches normal variadic semantics, with a strong feeling of similarity to \CCeleven variadic templates.
    773 As such, @ttype@ variables are also called \emph{argument packs}.
     780As such, @ttype@ variables are also called \newterm{argument packs}.
    774781
    775782Like variadic templates, the main way to manipulate @ttype@ polymorphic functions is via recursion.
    … …  
    843850\subsection{Implementation}
    844851
    845 Tuples are implemented in the \CFA translator via a transformation into \emph{generic types}.
     852Tuples are implemented in the \CFA translator via a transformation into \newterm{generic types}.
    846853For each $N$, the first time an $N$-tuple is seen in a scope a generic type with $N$ type parameters is generated, \eg:
    847854\begin{lstlisting}
    … …  
    894901Similarly, tuple member expressions are recursively expanded into a list of member access expressions.
    895902
    896 Expressions that may contain side effects are made into \emph{unique expressions} before being expanded by the flattening conversion.
     903Expressions that may contain side effects are made into \newterm{unique expressions} before being expanded by the flattening conversion.
    897904Each unique expression is assigned an identifier and is guaranteed to be executed exactly once:
    898905\begin{lstlisting}
    … …  
    10811088% In object-oriented programming, there is an implicit first parameter, often names @self@ or @this@, which is elided.
    10821089% In any programming language, some functions have a naturally close relationship with a particular data type.
    1083 % Object-oriented programming allows this close relationship to be codified in the language by making such functions \emph{class methods} of their related data type.
     1090% Object-oriented programming allows this close relationship to be codified in the language by making such functions \newterm{class methods} of their related data type.
    10841091% Class methods have certain privileges with respect to their associated data type, notably un-prefixed access to the fields of that data type.
    10851092% When writing C functions in an object-oriented style, this un-prefixed access is swiftly missed, as access to fields of a @Foo* f@ requires an extra three characters @f->@ every time, which disrupts coding flow and clutters the produced code.
    … …  
    11951202C declaration syntax is notoriously confusing and error prone.
    11961203For example, many C programmers are confused by a declaration as simple as:
    1197 \begin{flushleft}
     1204\begin{cquote}
    11981205\lstDeleteShortInline@%
    11991206\begin{tabular}{@{}ll@{}}
    … …  
    12051212\end{tabular}
    12061213\lstMakeShortInline@%
    1207 \end{flushleft}
     1214\end{cquote}
    12081215Is this an array of 5 pointers to integers or a pointer to an array of 5 integers?
    1209 The fact this declaration is unclear to many C programmers means there are productivity and safety issues even for basic programs.
     1216If there is any doubt, it implies productivity and safety issues even for basic programs.
    12101217Another example of confusion results from the fact that a routine name and its parameters are embedded within the return type, mimicking the way the return value is used at the routine's call site.
    12111218For example, a routine returning a pointer to an array of integers is defined and used in the following way:
    … …  
    12211228In the following example, \R{red} is the base type and \B{blue} is qualifiers.
    12221229The \CFA declarations move the qualifiers to the left of the base type, \ie move the blue to the left of the red, while the qualifiers have the same meaning but are ordered left to right to specify a variable's type.
    1223 \begin{quote}
     1230\begin{cquote}
    12241231\lstDeleteShortInline@%
    12251232\lstset{moredelim=**[is][\color{blue}]{+}{+}}
    … …  
    12391246\end{tabular}
    12401247\lstMakeShortInline@%
    1241 \end{quote}
     1248\end{cquote}
    12421249The only exception is bit field specification, which always appear to the right of the base type.
    1243 % Specifically, the character ©*© is used to indicate a pointer, square brackets ©[©\,©]© are used to represent an array or function return value, and parentheses ©()© are used to indicate a routine parameter.
     1250% Specifically, the character @*@ is used to indicate a pointer, square brackets @[@\,@]@ are used to represent an array or function return value, and parentheses @()@ are used to indicate a routine parameter.
    12441251However, unlike C, \CFA type declaration tokens are distributed across all variables in the declaration list.
    1245 For instance, variables ©x© and ©y© of type pointer to integer are defined in \CFA as follows:
    1246 \begin{quote}
     1252For instance, variables @x@ and @y@ of type pointer to integer are defined in \CFA as follows:
     1253\begin{cquote}
    12471254\lstDeleteShortInline@%
    12481255\begin{tabular}{@{}l@{\hspace{3em}}l@{}}
    … …  
    12571264\end{tabular}
    12581265\lstMakeShortInline@%
    1259 \end{quote}
     1266\end{cquote}
    12601267The downside of this semantics is the need to separate regular and pointer declarations:
    1261 \begin{quote}
     1268\begin{cquote}
    12621269\lstDeleteShortInline@%
    12631270\begin{tabular}{@{}l@{\hspace{3em}}l@{}}
    … …  
    12741281\end{tabular}
    12751282\lstMakeShortInline@%
    1276 \end{quote}
     1283\end{cquote}
    12771284which is prescribing a safety benefit.
    12781285Other examples are:
    1279 \begin{quote}
     1286\begin{cquote}
    12801287\lstDeleteShortInline@%
    12811288\begin{tabular}{@{}l@{\hspace{3em}}l@{\hspace{2em}}l@{}}
    … …  
    13151322\end{tabular}
    13161323\lstMakeShortInline@%
    1317 \end{quote}
    1318 
    1319 All type qualifiers, \eg ©const©, ©volatile©, etc., are used in the normal way with the new declarations and also appear left to right, \eg:
    1320 \begin{quote}
     1324\end{cquote}
     1325
     1326All type qualifiers, \eg @const@, @volatile@, etc., are used in the normal way with the new declarations and also appear left to right, \eg:
     1327\begin{cquote}
    13211328\lstDeleteShortInline@%
    13221329\begin{tabular}{@{}l@{\hspace{1em}}l@{\hspace{1em}}l@{}}
    … …  
    13381345\end{tabular}
    13391346\lstMakeShortInline@%
    1340 \end{quote}
    1341 All declaration qualifiers, \eg ©extern©, ©static©, etc., are used in the normal way with the new declarations but can only appear at the start of a \CFA routine declaration,\footnote{\label{StorageClassSpecifier}
     1347\end{cquote}
     1348All declaration qualifiers, \eg @extern@, @static@, etc., are used in the normal way with the new declarations but can only appear at the start of a \CFA routine declaration,\footnote{\label{StorageClassSpecifier}
    13421349The placement of a storage-class specifier other than at the beginning of the declaration specifiers in a declaration is an obsolescent feature.~\cite[\S~6.11.5(1)]{C11}} \eg:
    1343 \begin{quote}
     1350\begin{cquote}
    13441351\lstDeleteShortInline@%
    13451352\begin{tabular}{@{}l@{\hspace{3em}}l@{\hspace{2em}}l@{}}
    … …  
    13611368\end{tabular}
    13621369\lstMakeShortInline@%
    1363 \end{quote}
    1364 
    1365 The new declaration syntax can be used in other contexts where types are required, \eg casts and the pseudo-routine ©sizeof©:
    1366 \begin{quote}
     1370\end{cquote}
     1371
     1372The new declaration syntax can be used in other contexts where types are required, \eg casts and the pseudo-routine @sizeof@:
     1373\begin{cquote}
    13671374\lstDeleteShortInline@%
    13681375\begin{tabular}{@{}l@{\hspace{3em}}l@{}}
    13691376\multicolumn{1}{c@{\hspace{3em}}}{\textbf{\CFA}}        & \multicolumn{1}{c}{\textbf{C}}        \\
    13701377\begin{cfa}
    1371 y = (`* int`)x;
    1372 i = sizeof(`[ 5 ] * int`);
     1378y = (* int)x;
     1379i = sizeof([ 5 ] * int);
    13731380\end{cfa}
    13741381&
    13751382\begin{cfa}
    1376 y = (`int *`)x;
    1377 i = sizeof(`int * [ 5 ]`);
     1383y = (int *)x;
     1384i = sizeof(int * [ 5 ]);
    13781385\end{cfa}
    13791386\end{tabular}
    13801387\lstMakeShortInline@%
    1381 \end{quote}
     1388\end{cquote}
    13821389
    13831390Finally, new \CFA declarations may appear together with C declarations in the same program block, but cannot be mixed within a specific declaration.
    13841391Therefore, a programmer has the option of either continuing to use traditional C declarations or take advantage of the new style.
    1385 Clearly, both styles need to be supported for some time due to existing C-style header-files, particularly for UNIX systems.
     1392Clearly, both styles need to be supported for some time due to existing C-style header-files, particularly for UNIX-like systems.
    13861393
    13871394
    13881395\subsection{References}
    13891396
    1390 All variables in C have an \emph{address}, a \emph{value}, and a \emph{type}; at the position in the program's memory denoted by the address, there exists a sequence of bits (the value), with the length and semantic meaning of this bit sequence defined by the type.
    1391 The C type system does not always track the relationship between a value and its address; a value that does not have a corresponding address is called a \emph{rvalue} (for ``right-hand value''), while a value that does have an address is called a \emph{lvalue} (for ``left-hand value''); in @int x; x = 42;@ the variable expression @x@ on the left-hand-side of the assignment is a lvalue, while the constant expression @42@ on the right-hand-side of the assignment is a rvalue.
    1392 Which address a value is located at is sometimes significant; the imperative programming paradigm of C relies on the mutation of values at specific addresses.
    1393 Within a lexical scope, lvalue exressions can be used in either their \emph{address interpretation} to determine where a mutated value should be stored or in their \emph{value interpretation} to refer to their stored value; in @x = y;@ in @{ int x, y = 7; x = y; }@, @x@ is used in its address interpretation, while y is used in its value interpretation.
    1394 Though this duality of interpretation is useful, C lacks a direct mechanism to pass lvalues between contexts, instead relying on \emph{pointer types} to serve a similar purpose.
    1395 In C, for any type @T@ there is a pointer type @T*@, the value of which is the address of a value of type @T@; a pointer rvalue can be explicitly \emph{dereferenced} to the pointed-to lvalue with the dereference operator @*?@, while the rvalue representing the address of a lvalue can be obtained with the address-of operator @&?@.
     1397All variables in C have an \newterm{address}, a \newterm{value}, and a \newterm{type};
     1398at the position in the program's memory denoted by the address, there exists a sequence of bits (the value), with the length and semantic meaning of this bit sequence defined by the type.
     1399The C type-system does not always track the relationship between a value and its address;
     1400a value that does not have a corresponding address is called a \newterm{rvalue} (for ``right-hand value''), while a value that does have an address is called a \newterm{lvalue} (for ``left-hand value'').
     1401For example, in @int x; x = 42;@ the variable expression @x@ on the left-hand-side of the assignment is a lvalue, while the constant expression @42@ on the right-hand-side of the assignment is a rvalue.
     1402In imperative programming, the address of a value is used for both reading and writing (mutating) a value.
     1403
     1404Within a lexical scope, lvalue expressions have an \newterm{address interpretation} for writing a value or a \newterm{value interpretation} to read a value.
     1405For example, in @x = y@, @x@ has an address interpretation, while @y@ has a value interpretation.
     1406Though this duality of interpretation is useful, C lacks a direct mechanism to pass lvalues between contexts, instead relying on \newterm{pointer types} to serve a similar purpose.
     1407In C, for any type @T@ there is a pointer type @T *@, the value of which is the address of a value of type @T@.
     1408A pointer rvalue can be explicitly \newterm{dereferenced} to the pointed-to lvalue with the dereference operator @*?@, while the rvalue representing the address of a lvalue can be obtained with the address-of operator @&?@.
    13961409
    13971410\begin{cfa}
    13981411int x = 1, y = 2, * p1, * p2, ** p3;
    1399 p1 = &x;  $\C{// p1 points to x}$
    1400 p2 = &y;  $\C{// p2 points to y}$
    1401 p3 = &p1;  $\C{// p3 points to p1}$
     1412p1 = &x;                                                                $\C{// p1 points to x}$
     1413p2 = &y;                                                                $\C{// p2 points to y}$
     1414p3 = &p1;                                                               $\C{// p3 points to p1}$
    14021415*p2 = ((*p1 + *p2) * (**p3 - *p1)) / (**p3 - 15);
    14031416\end{cfa}
    … …  
    14051418Unfortunately, the dereference and address-of operators introduce a great deal of syntactic noise when dealing with pointed-to values rather than pointers, as well as the potential for subtle bugs.
    14061419For both brevity and clarity, it would be desirable to have the compiler figure out how to elide the dereference operators in a complex expression such as the assignment to @*p2@ above.
    1407 However, since C defines a number of forms of \emph{pointer arithmetic}, two similar expressions involving pointers to arithmetic types (\eg @*p1 + x@ and @p1 + x@) may each have well-defined but distinct semantics, introducing the possibility that a user programmer may write one when they mean the other, and precluding any simple algorithm for elision of dereference operators.
     1420However, since C defines a number of forms of \newterm{pointer arithmetic}, two similar expressions involving pointers to arithmetic types (\eg @*p1 + x@ and @p1 + x@) may each have well-defined but distinct semantics, introducing the possibility that a user programmer may write one when they mean the other, and precluding any simple algorithm for elision of dereference operators.
    14081421To solve these problems, \CFA introduces reference types @T&@; a @T&@ has exactly the same value as a @T*@, but where the @T*@ takes the address interpretation by default, a @T&@ takes the value interpretation by default, as below:
    14091422
    14101423\begin{cfa}
    1411 inx x = 1, y = 2, & r1, & r2, && r3;
     1424int x = 1, y = 2, & r1, & r2, && r3;
    14121425&r1 = &x;  $\C{// r1 points to x}$
    14131426&r2 = &y;  $\C{// r2 points to y}$
    … …  
    14311444This allows \CFA references to be default-initialized (\eg to a null pointer), and also to point to different addresses throughout their lifetime.
    14321445This rebinding is accomplished without adding any new syntax to \CFA, but simply by extending the existing semantics of the address-of operator in C.
     1446
    14331447In C, the address of a lvalue is always a rvalue, as in general that address is not stored anywhere in memory, and does not itself have an address.
    14341448In \CFA, the address of a @T&@ is a lvalue @T*@, as the address of the underlying @T@ is stored in the reference, and can thus be mutated there.
    … …  
    14441458        if @L@ is an lvalue of type {@T &@$_1 \cdots$@ &@$_l$} where $l \ge 0$ references (@&@ symbols) then @&L@ has type {@T `*`&@$_{\color{red}1} \cdots$@ &@$_{\color{red}l}$}, \\ \ie @T@ pointer with $l$ references (@&@ symbols).
    14451459\end{itemize}
    1446 
    14471460Since pointers and references share the same internal representation, code using either is equally performant; in fact the \CFA compiler converts references to pointers internally, and the choice between them in user code can be made based solely on convenience.
     1461
    14481462By analogy to pointers, \CFA references also allow cv-qualifiers:
    14491463
    … …  
    14641478
    14651479More generally, this initialization of references from lvalues rather than pointers is an instance of a ``lvalue-to-reference'' conversion rather than an elision of the address-of operator; this conversion can actually be used in any context in \CFA an implicit conversion would be allowed.
    1466 Similarly, use of a the value pointed to by a reference in an rvalue context can be thought of as a ``reference-to-rvalue'' conversion, and \CFA also includes a qualifier-adding ``reference-to-reference'' conversion, analagous to the @T *@ to @const T *@ conversion in standard C.
     1480Similarly, use of a the value pointed to by a reference in an rvalue context can be thought of as a ``reference-to-rvalue'' conversion, and \CFA also includes a qualifier-adding ``reference-to-reference'' conversion, analogous to the @T *@ to @const T *@ conversion in standard C.
    14671481The final reference conversion included in \CFA is ``rvalue-to-reference'' conversion, implemented by means of an implicit temporary.
    14681482When an rvalue is used to initialize a reference, it is instead used to initialize a hidden temporary value with the same lexical scope as the reference, and the reference is initialized to the address of this temporary.
    14691483This allows complex values to be succinctly and efficiently passed to functions, without the syntactic overhead of explicit definition of a temporary variable or the runtime cost of pass-by-value.
    1470 \CC allows a similar binding, but only for @const@ references; the more general semantics of \CFA are an attempt to avoid the \emph{const hell} problem, in which addition of a @const@ qualifier to one reference requires a cascading chain of added qualifiers.
     1484\CC allows a similar binding, but only for @const@ references; the more general semantics of \CFA are an attempt to avoid the \newterm{const hell} problem, in which addition of a @const@ qualifier to one reference requires a cascading chain of added qualifiers.
     1485
    14711486
    14721487\subsection{Constructors and Destructors}
    … …  
    14741489One of the strengths of C is the control over memory management it gives programmers, allowing resource release to be more consistent and precisely timed than is possible with garbage-collected memory management.
    14751490However, this manual approach to memory management is often verbose, and it is useful to manage resources other than memory (\eg file handles) using the same mechanism as memory.
    1476 \CC is well-known for an approach to manual memory management that addresses both these issues, Resource Aquisition Is Initialization (RAII), implemented by means of special \emph{constructor} and \emph{destructor} functions; we have implemented a similar feature in \CFA.
     1491\CC is well-known for an approach to manual memory management that addresses both these issues, Resource Aquisition Is Initialization (RAII), implemented by means of special \newterm{constructor} and \newterm{destructor} functions; we have implemented a similar feature in \CFA.
    14771492While RAII is a common feature of object-oriented programming languages, its inclusion in \CFA does not violate the design principle that \CFA retain the same procedural paradigm as C.
    14781493In particular, \CFA does not implement class-based encapsulation: neither the constructor nor any other function has privileged access to the implementation details of a type, except through the translation-unit-scope method of opaque structs provided by C.
    … …  
    15061521\end{cfa}
    15071522
    1508 In the example above, a \emph{default constructor} (\ie one with no parameters besides the @this@ parameter) and destructor are defined for the @Array@ struct, a dynamic array of @int@.
    1509 @Array@ is an example of a \emph{managed type} in \CFA, a type with a non-trivial constructor or destructor, or with a field of a managed type.
     1523In the example above, a \newterm{default constructor} (\ie one with no parameters besides the @this@ parameter) and destructor are defined for the @Array@ struct, a dynamic array of @int@.
     1524@Array@ is an example of a \newterm{managed type} in \CFA, a type with a non-trivial constructor or destructor, or with a field of a managed type.
    15101525As in the example, all instances of managed types are implicitly constructed upon allocation, and destructed upon deallocation; this ensures proper initialization and cleanup of resources contained in managed types, in this case the @data@ array on the heap.
    15111526The exact details of the placement of these implicit constructor and destructor calls are omitted here for brevity, the interested reader should consult \cite{Schluntz17}.
    15121527
    15131528Constructor calls are intended to seamlessly integrate with existing C initialization syntax, providing a simple and familiar syntax to veteran C programmers and allowing constructor calls to be inserted into legacy C code with minimal code changes.
    1514 As such, \CFA also provides syntax for \emph{copy initialization} and \emph{initialization parameters}:
     1529As such, \CFA also provides syntax for \newterm{copy initialization} and \newterm{initialization parameters}:
    15151530
    15161531\begin{cfa}
    … …  
    15271542In addition to initialization syntax, \CFA provides two ways to explicitly call constructors and destructors.
    15281543Explicit calls to constructors double as a placement syntax, useful for construction of member fields in user-defined constructors and reuse of large storage allocations.
    1529 While the existing function-call syntax works for explicit calls to constructors and destructors, \CFA also provides a more concise \emph{operator syntax} for both:
     1544While the existing function-call syntax works for explicit calls to constructors and destructors, \CFA also provides a more concise \newterm{operator syntax} for both:
    15301545
    15311546\begin{cfa}
    … …  
    15441559For compatibility with C, a copy constructor from the first union member type is also defined.
    15451560For @struct@ types, each of the four functions are implicitly defined to call their corresponding functions on each member of the struct.
    1546 To better simulate the behaviour of C initializers, a set of \emph{field constructors} is also generated for structures.
     1561To better simulate the behaviour of C initializers, a set of \newterm{field constructors} is also generated for structures.
    15471562A constructor is generated for each non-empty prefix of a structure's member-list which copy-constructs the members passed as parameters and default-constructs the remaining members.
    15481563To allow users to limit the set of constructors available for a type, when a user declares any constructor or destructor, the corresponding generated function and all field constructors for that type are hidden from expression resolution; similarly, the generated default constructor is hidden upon declaration of any constructor.
    … …  
    15501565
    15511566In rare situations user programmers may not wish to have constructors and destructors called; in these cases, \CFA provides an ``escape hatch'' to not call them.
    1552 If a variable is initialized using the syntax \lstinline|S x @= {}| it will be an \emph{unmanaged object}, and will not have constructors or destructors called.
     1567If a variable is initialized using the syntax \lstinline|S x @= {}| it will be an \newterm{unmanaged object}, and will not have constructors or destructors called.
    15531568Any C initializer can be the right-hand side of an \lstinline|@=| initializer, \eg  \lstinline|Array a @= { 0, 0x0 }|, with the usual C initialization semantics.
    15541569In addition to the expressive power, \lstinline|@=| provides a simple path for migrating legacy C code to \CFA, by providing a mechanism to incrementally convert initializers; the \CFA design team decided to introduce a new syntax for this escape hatch because we believe that our RAII implementation will handle the vast majority of code in a desirable way, and we wished to maintain familiar syntax for this common case.
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