compiler-errors - 如何定义指向相同名称的静态类方法的全局宏？

Question

我有以下MQL4/5代码:

class MQL4 {
public:
  static double Ask() {
    MqlTick _tick;
    SymbolInfoTick(_Symbol, _tick);
    return _tick.ask;
    // Overriding Ask variable to become a function call.
    #define Ask MQL4::Ask()
  }

};

void start() {
  double ask = Ask; // line 14
};

但是，根据错误，它无法在MQL4或MQL5下编译:

> mql /s /mql5 Test.mqh
MQL4/MQL5 Compiler build 1162 (02 Jul 2015)
Test.mqh : information: Checking 'Test.mqh'
Test.mqh(14,16) : error 320: 'Ask' - too complex, simplify the macro
Test.mqh(14,16) : error 239: '::' - syntax error
Test.mqh(14,16) : error 239: '::' - syntax error
Test.mqh(14,16) : error 239: '::' - syntax error
Test.mqh(14,16) : error 239: '::' - syntax error
Test.mqh(14,16) : error 239: '::' - syntax error
Test.mqh(14,16) : error 239: '::' - syntax error
Test.mqh(14,16) : error 239: '::' - syntax error
Test.mqh(14,16) : error 149: unexpected token
Test.mqh(14,16) : error 149: ')' - unexpected token
Test.mqh(14,16) : error 157: 'MQL4' - expression expected
Test.mqh(14,10) : warning 31: variable 'ask' not used
 : information: Result 11 error(s), 1 warning(s)

与最新的1498版本相同的错误。

基本上是说 Ask宏太复杂了。虽然在将 Ask() 方法重命名为 GetAsk() 并更新宏定义时效果很好，但是我想了解是否有其他解决方案而不必重命名。

有什么我可以定义 macro substitution的语法，它可以理解以下宏:

#define Ask MQL4::Ask()

无需重命名，同时仍将其保留在静态类方法中？

Answer 1

是的，但是……，不! #define替换可以正常工作，但是...但是 Ask 是保留字，这会使编译器感到困惑。

实际上，问题出在编译器预处理器的功能有限，而不是 .method() 的“相同名称”。

非参数和参数替代功能 #define 指令均已测试到已发布的MQL4/5语言语法的极限。
Case[6]最终证明，
Class.<_method_>() 可以具有相同的名称 .Ask() ，但不能与 #define -s <_literal_symbol_to_substitute_>相同

//+------------------------------------------------------------------+
//|                                   StackOverflow__test_DEFINE.mq4 |
//|                                       Copyright © 1987-2017 [ME] |
//|                                                       nowhere.no |
//+------------------------------------------------------------------+
#property strict
 // -------------------------------------------------------------------------------------------------------------------------
/*                                                       // [Case[1] FAILS BELOW
#define               Ask MQL4::Ask( True )              // [Case[1] // Overriding Ask variable to become a function call. */

class MQL4 { 
     public:
     static double Ask( bool FakeSyntaxSUGAR = False ) { // [Case[1] FAILS HERE TO PROCESS EXPANDED PRE-PROCESSOR #define SUBSTITUTION]
                        MqlTick _tick;
                        SymbolInfoTick( _Symbol,
                                        _tick
                                        );
                        return _tick.ask;
         }
};

//+------------------------------------------------------------------+
//| Script program start function                                    |
//+------------------------------------------------------------------+

void OnStart() {

 // -------------------------------------------------------------------------------------------------------------------------
/*                                                       // [Case[2] FAILS
#define               Ask MQL4::Ask( True )              // [Case[2] // Overriding Ask variable to become a function call. */
  // double ask     = Ask;                               // [Case[2] FAILS TO COMPILE, ERROR on "Ask;"]


  // ------------------------------------------------------------------------------------------------------------------------
  // double askMQL4 = MQL4::Ask( True );                 // [Case[3] OK    TO COMPILE EXPLICIT CALL TO an explicit absolute reference to a method-name]


 // -------------------------------------------------------------------------------------------------------------------------
/*                                                       // [Case[4] OK */
     MQL4* aPtrToINSTANCE = new MQL4();                  // [Case[4]
  // double askINST = aPtrToINSTANCE.Ask( False );       // [Case[4] OK    TO COMPILE EXPLICIT CALL TO aPtrToINSTANCE-referred instance of Class ]

 // -------------------------------------------------------------------------------------------------------------------------
/*                                                       // [Case[5] FAILS
#define               Ask aPtrToINSTANCE.Ask( False )    // [Case[5] */
  // double askINST = Ask;                               // [Case[5] FAILS TO PRE-PROCESS #define HERE ]


 // -------------------------------------------------------------------------------------------------------------------------
/*                                                       // [Case[6] OK */
#define               Ask_with_SomeOtherDEFINE_NAME aPtrToINSTANCE.Ask( False )
     double askINST = Ask_with_SomeOtherDEFINE_NAME;     // [Case[6] OK    TO CALL THE .Ask() METHOD AS THE PRE-PROCESSOR <_SYMBOL_TO_SUBSTITE_> WAS #define-d AS NON-COLLIDING]

//    **   *   ****        ****        *****        *****
//    ***  *  **   *      **   *       **           **   *
//    ** * *  **   *      **   *       ***          **    *
//    **  **  **   *      ** * *       **           **   * 
//    **   *   ****  **    ****   **   *****  **    *****  **
//                   *         *  
}; 
// ------------------------------------------------------------------

结语:

As I have posted somewhere in some other MQL4-posts, after having some extensive testing of the capabilities available from the #define directive based pre-compiler substitutions ( for version management purposes et al ), I could but draw a conclusion to try to avoid using this feature, as the resulting problems were far more expensive ( surprising string-handling limitations, uncertainties about the continuing language creeps, unpredictable results of syntax-sugar tricks after next Build releases etc. ) than beneficial for the purposes intended.