Changeset 7ab24fef
- Timestamp:
- Aug 4, 2024, 2:35:13 PM (3 months ago)
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- master
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- 2514d3d7, 5f210c0
- Parents:
- b59c21a (diff), 748877f (diff)
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- doc/theses/jiada_liang_MMath
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doc/theses/jiada_liang_MMath/CEnum.tex
rb59c21a r7ab24fef 1 \chapter{C Enumeration in CFA}1 \chapter{C Enumeration in \CFA} 2 2 3 3 \CFA supports legacy C enumeration using the same syntax for backwards compatibility. 4 C-style Enumeration in \CFA language are called \newterm{C Enumeration} or \newterm{C Enum}. 5 The semantics of C Enumeration is mostly consistent with C with more restrictive typing. 6 \CFA also extends C Enumeration by adding a number of new features that bring enumerations aligns with other modern programming languages. 7 Any enumeration extensions must be intuitive to C programmers both in syntax and semantics. 8 The following sections detail all of my new contributions to enumerations in \CFA. 4 A C-style enumeration in \CFA is called a \newterm{C Enum}. 5 The semantics of the C Enum is mostly consistent with C with some restrictions. 6 The following sections detail all of my new contributions to C Enums. 7 9 8 10 9 \section{Enumerator Visibility} … … 12 11 13 12 In C, unscoped enumerators present a \newterm{naming problem} when multiple enumeration types appear in the same scope with duplicate enumerator names. 13 \begin{cfa} 14 enum E1 { First, Second, Third, Fourth }; 15 enum E2 { @Fourth@, @Third@, @Second@, @First@ }; $\C{// same enumerator names}$ 16 \end{cfa} 14 17 There is no mechanism in C to resolve these naming conflicts other than renaming one of the duplicates, which may be impossible if the conflict comes from system include files. 15 18 16 19 The \CFA type-system allows extensive overloading, including enumerators. 17 Furthermore, \CFA uses the environment, such as the left-hand of assignment and function arguments, to pinpoint the best overloaded name. 18 \VRef[Figure]{f:EnumeratorVisibility} shows enumeration overloading and how qualification and casting are used to disambiguate ambiguous situations. 19 \CFA overloading allows programmers to use the most meaningful names without fear of name clashes within a program or from external sources, like include files. 20 Experience from \CFA developers is that the type system implicitly and correctly disambiguates the majority of overloaded names. 21 That is, it is rare to get an incorrect selection or ambiguity, even among hundreds of overloaded variables and functions, that requires disambiguation using qualification or casting. 20 Hence, most ambiguities among C enumerators are implicitly resolved by the \CFA type system, possibly without any programmer knowledge of the conflict. 21 In addition, C Enum qualification is added, exactly like aggregate field-qualification, to disambiguate. 22 \VRef[Figure]{f:EnumeratorVisibility} shows how resolution, qualification, and casting are used to disambiguate situations for enumerations @E1@ and @E2@. 22 23 23 24 \begin{figure} 24 25 \begin{cfa} 25 enum E1 { First, Second, Third, Fourth };26 enum E2 { @Fourth@, @Third@, @Second@, @First@ }; $\C{// same enumerator names}$27 26 E1 f() { return Third; } $\C{// overload functions with different return types}$ 28 27 E2 f() { return Fourth; } … … 42 41 \end{figure} 43 42 44 \CFA overloading allows programmers to use the most meaningful names without fear of name clashes within a program or from external sources, like include files.45 Experience from \CFA developers is that the type system implicitly and correctly disambiguates the majority of overloaded names, \ie it is rare to get an incorrect selection or ambiguity, even among hundreds of overloaded variables and functions.46 Any ambiguity can be resolved using qualification or casting.47 48 43 49 44 \section{Enumerator Scoping} 50 45 51 A n enumerationcan be scoped, using @'!'@, so the enumerator constants are not projected into the enclosing scope.46 A C Enum can be scoped, using @'!'@, so the enumerator constants are not projected into the enclosing scope. 52 47 \begin{cfa} 53 48 enum Week @!@ { Mon, Tue, Wed, Thu = 10, Fri, Sat, Sun }; … … 61 56 rgb = @RGB.@Blue; 62 57 \end{cfa} 63 {\color{red}@***@}It is possible to toggle back to unscoped using the \CFA @with@ clause/statement (see also \CC \lstinline[language=c++]{using enum} in Section~\ref{s:C++RelatedWork}). 58 % feature unimplemented 59 It is possible to toggle back to unscoped using the \CFA @with@ auto-qualification clause/statement (see also \CC \lstinline[language=c++]{using enum} in Section~\ref{s:C++RelatedWork}). 64 60 \begin{cfa} 65 61 with ( @Week@, @RGB@ ) { $\C{// type names}$ … … 70 66 As in Section~\ref{s:EnumeratorVisibility}, opening multiple scoped enumerations in a @with@ can result in duplicate enumeration names, but \CFA implicit type resolution and explicit qualification/casting handle this localized scenario. 71 67 68 72 69 \section{Type Safety} 73 70 74 71 As in Section~\ref{s:Usage}, C's implicit bidirectional conversion between enumeration and integral type raises a safety concern. 75 In \CFA, the conversion is unidirectional: 76 % disallows an implicit conversion from integral type to enumeration, and conversion between different C enumeration type. 77 % It loses some degree of its backward compatibility to C, in exchange for type safety. 78 an enumeration can be implicitly converted into an integral type, with an associated @safe@ conversion cost. 79 But an integral type cannot be implicitly converted into a C enumeration. (Conversion Cost is Infinity.) 72 In \CFA, the conversion is changed to unidirectional: an enumeration can be implicitly converted into an integral type, with an associated @safe@ conversion cost. 73 But an integral type cannot be implicitly converted into a C enumeration because the conversion cost is set to @infinity@. 80 74 \begin{cfa} 81 enum Bird { Peng in, Robin, Eagle };75 enum Bird { Penguin, Robin, Eagle }; 82 76 enum Fish { Shark, Salmon, Whale }; 83 77 84 int i = Robin; $\C{// Allow, implicitly converts to 1}$85 @enum Bird bird = Shark;@ $\C{// Disallow }$86 @enum Bird bird = 1;@ $\C{// Disallow }$78 int i = Robin; $\C{// allow, implicitly converts to 1}$ 79 enum Bird @bird = 1;@ $\C{// disallow }$ 80 enum Bird @bird = Shark;@ $\C{// disallow }$ 87 81 \end{cfa} 88 As a workaround, \CFA allows an explicit cast to an enumeration, turning an integral type to an enumeration that can be used in assignment or function argument, 89 in which case \CFA treats C enuemration as its underlying integral type. In such cases, it is up to user to ensure program correctness. 82 It is now up to the programmer to insert an explicit cast to force the assignment. 90 83 \begin{cfa} 91 @enum Bird bird = (Bird) Shark@ 92 @enum Bird bird = (Bird) 1;@84 enum Bird bird = @(Bird)@1; 85 enum Bird bird = @(Bird)@Shark 93 86 \end{cfa} 87 88 Note, \CC has the same safe restriction~\cite[C.1.5.7.2]{C++} and provides the same workaround cast. 89 \begin{description}[parsep=0pt] 90 \item[Change:] \CC objects of enumeration type can only be assigned values of the same enumeration type. 91 In C, objects of enumeration type can be assigned values of any integral type. 92 Example: 93 \begin{cfa} 94 enum color { red, blue, green }; 95 color c = 1; $\C{// valid C, invalid \CC}$ 96 \end{cfa} 97 \item[Rationale:] The type-safe nature of \CC. 98 \item[Effect on original feature:] Deletion of semantically well-defined feature. 99 \item[Difficulty of converting:] Syntactic transformation. (The type error produced by the assignment can be 100 automatically corrected by applying an explicit cast.) 101 \item[How widely used:] Common. 102 \end{description} 103 104 \begin{comment} 105 \begin{description}[parsep=0pt] 106 \item[Change:] In \CC, the type of an enumerator is its enumeration. 107 In C, the type of an enumerator is @int@. 108 Example: 109 \begin{cfa} 110 enum e { A }; 111 sizeof(A) == sizeof(int) $\C{// in C}$ 112 sizeof(A) == sizeof(e) $\C{// in \CC}$ 113 /* and sizeof(int) is not necessary equal to sizeof(e) */ 114 \end{cfa} 115 \item[Rationale:] In \CC, an enumeration is a distinct type. 116 \item[Effect on original feature:] Change to semantics of well-defined feature. 117 \item[Difficulty of converting:] Semantic transformation. 118 \item[How widely used:] Seldom. The only time this affects existing C code is when the size of an enumerator is 119 taken. Taking the size of an enumerator is not a common C coding practice. 120 \end{description} 121 \end{comment} -
doc/theses/jiada_liang_MMath/background.tex
rb59c21a r7ab24fef 240 240 \section{\CFA} 241 241 242 \CFA in \emph{not} an object-oriented programming-language, \ie functions cannot be nested in aggregate types, and hence, there is no receive notation for calling functions, \eg @obj.method(...)@, where the first argument proceeds the call. 243 The following section provide short descriptions of \CFA features mentioned further in the thesis. 242 \CFA in \emph{not} an object-oriented programming-language, \ie functions cannot be nested in aggregate types, and hence, there is no \newterm{receiver} notation for calling functions, \eg @obj.method(...)@, where the first argument proceeds the call and becomes an implicit first (\lstinline[language=C++]{this}) parameter. 243 The following sections provide short descriptions of \CFA features needed further in the thesis. 244 Other \CFA features are presented in-situ with short explanations, or no explanation because the feature is obvious to C programmers. 245 246 247 \subsection{Overloading} 248 249 Overloading allows programmers to use the most meaningful names without fear of name clashes within a program or from external sources, like include files. 250 \begin{quote} 251 There are only two hard things in Computer Science: cache invalidation and naming things. --- Phil Karlton 252 \end{quote} 253 Experience from \CC and \CFA developers is that the type system implicitly and correctly disambiguates the majority of overloaded names, \ie it is rare to get an incorrect selection or ambiguity, even among hundreds of overloaded (variables and) functions. 254 In many cases, a programmer has no idea there are name clashes, as they are silently resolved, simplifying the development process. 255 Depending on the language, ambiguous cases are resolved using some form of qualification or casting. 244 256 245 257 … … 273 285 Here, there is a perfect match for the call, @f( 'A' )@ with the number and parameter type of function (2). 274 286 275 Ada, Scala, and \CFA type-systems also use the return type in resolving a call .287 Ada, Scala, and \CFA type-systems also use the return type in resolving a call, to pinpoint the best overloaded name. 276 288 \begin{cfa} 277 289 int f( void ); $\C[1.75in]{// (4); overloaded on return type}$ … … 296 308 \end{cfa} 297 309 The \CFA type system simply treats overloaded variables as an overloaded function returning a value with no parameters. 310 Hence, no significant effort is required to support this feature. 298 311 299 312 … … 308 321 309 322 The prototype for the constructor/destructor are @void ?{}( T &, ... )@ and @void ^?{}( T &, ... )@, respectively. 310 The first parameter is logically, the \lstinline[language=C++]{this} or \lstinline[language=java]{self} in other object-oriented languages, and implicitly passed. 323 The first parameter is logically, the \lstinline[language=C++]{this} or \lstinline[language=Python]{self} in other object-oriented languages, and implicitly passed. 324 \VRef[Figure]{f:CFAConstructorDestructor} shows an example of creating and using a constructor and destructor. 325 Both constructor and destructor can be explicitly called to reuse a variable. 326 327 \begin{figure} 311 328 \begin{cfa} 312 329 struct Employee { … … 314 331 double salary; 315 332 }; 316 void @?{}@( Employee & this, char * name, double salary ) {317 this.name = aalloc( sizeof(name) );318 strcpy( this.name,name );319 this.salary =salary;320 } 321 void @^?{}@( Employee & this) {322 free( this.name );333 void @?{}@( Employee & emp, char * nname, double nsalary ) with( emp ) { // auto qualification 334 name = aalloc( sizeof(nname) ); 335 strcpy( name, nname ); 336 salary = nsalary; 337 } 338 void @^?{}@( Employee & emp ) { 339 free( emp.name ); 323 340 } 324 341 { 325 Employee name = { "Sara Schmidt", 20.5 }; 326 } // implicit destructor call 327 \end{cfa} 328 Both constructor and destructor can be explicitly called. 329 \begin{cfa} 330 Employee name = { "Sara Schmidt", 20.5 }; 331 ... // use name 332 ^?{}( name ); // de-initialize 333 ?{}( name, "Jack Smith", 10.5 }; // re-initialize 334 ... // use name 335 \end{cfa} 342 Employee emp = { "Sara Schmidt", 20.5 }; $\C{// initialize with implicit constructor call}$ 343 ... // use emp 344 ^?{}( emp ); $\C{// explicit de-initialize}$ 345 ?{}( emp, "Jack Smith", 10.5 ); $\C{// explicit re-initialize}$ 346 ... // use emp 347 } $\C{// de-initialize with implicit destructor call}$ 348 \end{cfa} 349 \caption{\CFA Constructor and Destructor} 350 \label{f:CFAConstructorDestructor} 351 \end{figure} 336 352 337 353
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