cpp foreach macro

showcase

1. EqualToAnyOf

   // 注意 递归单元
   EqualToAnyOf(3, 1, 2, 3); // 0 || (3 == 1) || (3 == 2) || (3 == 3) 
   

2. MAKE_ENUM

   MAKE_ENUM(EE,"name_prefix",E1,E2,E3);
   // 展开到
   enum class EE {E1, E2,E3 };
   const char *GetStr(EE e)
   {g
       switch (e)
       {
       case EE::E1:
           return "name_prefix" "E1";
       case EE::E2:
           return "name_prefix" "E2";
       case EE::E3:
           return "name_prefix" "E3";
       default:
           return "name_prefix" "";
       }
   };
   

介绍

// prototype
#define FOREACH(pps,...) ...
// acutually params 
#define FOREACH(pps,it_operator,...)

pps: 打包参数，形如 (arg1), (arg1,arg2)
it_operator: 迭代宏函数，如此使用：ite_operator(pps,it)
...: 迭代参数集合，展开后作为 ite_oprator的最后一个参数

实现

辅助宏函数

1. __Choose20th

   #define __Choose20th(_1, _2, _3, _4, _5, _6, _7, _8, _9, _10, _11, _12, _13,_14, _15, _16, _17, _18, _19, _20, ...) \
   _20
   

2. ID
   msvc默认的宏展开有一点区别于gcc like编译器，所以老是需要用ID去做展开

   #define ID(_1, ...) _1
   #define IDx(...) __VA_ARGS__
   

3. Callx + CallxPPS

   #define Callx(f, ...) IDx(f(__VA_ARGS__))
   #define CallxPPS(f, _1) IDx(f _1)
   

   两种形式的宏函数代理调用
   因为当我遇到 MacroFunc(IDx pps, otherArgs)时，外部套一层 IDx也无法使展开的pps作为分离参数传入MacroFunc

   感觉 ID只能辅助展开__VA_ARGS__,所以这里 Callx(MacroFunc, IDx pps, otherArgs) 将所有参数压缩成变长参数之后再由 Callx重新展开

过程

OK, finally.

Show me the code

#define __Choose20th(_1, _2, _3, _4, _5, _6, _7, _8, _9, _10, _11, _12, _13, _14, _15, _16, _17, _18, _19, _20, ...) _20
#define ID(_1, ...) _1
#define IDx(...) __VA_ARGS__
#define Callx(f, ...) IDx(f(__VA_ARGS__))
#define CallxPPS(f, _1) IDx(f _1)

#define FOREACH0(it_operator, pps)
#define FOREACH1(it_operator, pps, _1) IDx(it_operator(pps, _1) FOREACH0(it_operator, pps))
#define FOREACH2(it_operator, pps, _1, ...) IDx(it_operator(pps, _1) FOREACH1(it_operator, pps, __VA_ARGS__))
#define FOREACH3(it_operator, pps, _1, ...) IDx(it_operator(pps, _1) FOREACH2(it_operator, pps, __VA_ARGS__))
#define FOREACH4(it_operator, pps, _1, ...) IDx(it_operator(pps, _1) FOREACH3(it_operator, pps, __VA_ARGS__))
#define FOREACH5(it_operator, pps, _1, ...) IDx(it_operator(pps, _1) FOREACH4(it_operator, pps, __VA_ARGS__))
#define FOREACH6(it_operator, pps, _1, ...) IDx(it_operator(pps, _1) FOREACH5(it_operator, pps, __VA_ARGS__))
#define FOREACH7(it_operator, pps, _1, ...) IDx(it_operator(pps, _1) FOREACH6(it_operator, pps, __VA_ARGS__))
#define FOREACH8(it_operator, pps, _1, ...) IDx(it_operator(pps, _1) FOREACH7(it_operator, pps, __VA_ARGS__))
#define FOREACH9(it_operator, pps, _1, ...) IDx(it_operator(pps, _1) FOREACH8(it_operator, pps, __VA_ARGS__))
#define FOREACH10(it_operator, pps, _1, ...) IDx(it_operator(pps, _1) FOREACH9(it_operator, pps, __VA_ARGS__))
#define FOREACH11(it_operator, pps, _1, ...) IDx(it_operator(pps, _1) FOREACH10(it_operator, pps, __VA_ARGS__))
#define FOREACH(pps, ...)           \
    ID(__Choose30th(__VA_ARGS__,    \
FOREACH28, FOREACH27, FOREACH26, FOREACH25, FOREACH24, FOREACH23, FOREACH22, FOREACH21, FOREACH20, FOREACH19, FOREACH18, FOREACH17, FOREACH16, FOREACH15, FOREACH14, FOREACH13, FOREACH12, FOREACH11, FOREACH10, FOREACH9, FOREACH8, FOREACH7, FOREACH6, FOREACH5, FOREACH4, FOREACH3, FOREACH2, FOREACH1,                     FOREACH0))                                                                                         \
    IDx((pps, __VA_ARGS__))

Use Case

1. EqualToAnyOf

#define __EqualToPlain(x, y) || (x == y)
#define __EqualToPacket(px, y) Callx(__EqualToPlain, IDx px, y)
#define EqualToAnyOf(val, ...) 0 FOREACH(__EqualToPacket, (val), __VA_ARGS__)

1. MAKE_ENUM

#define MAKE_ENUM_Declare(ClsName,...) enum class ClsName{__VA_ARGS__};
#define MAKE_ENUM_ITEM_Begin(ClsName) \
    const char *GetStr(ClsName e)     \
    {                                 \
        switch (e)                    \
        {
#define MAKE_ENUM_ITEM(ClsName, Prefix, name) \
    case ClsName::name:                       \
        return Prefix #name;
// #define MAKE_ENUM_ITEM_PPS(pps, item) CallxPPS( Callx,(MAKE_ENUM_ITEM, IDx pps, item))
#define MAKE_ENUM_ITEM_PPS(pps, item) Callx(MAKE_ENUM_ITEM, IDx pps, item)
#define MAKE_ENUM_ITEM_End(ClsName, Prefix) \
    default:                                \
        return Prefix "";                   \
        }                                   \
        }
#define MAKE_ENUM(ClsName, Prefix, ...)                               \
    MAKE_ENUM_Declare(ClsName, __VA_ARGS__)                           \
    MAKE_ENUM_ITEM_Begin(ClsName)                                     \
    IDx(FOREACH(MAKE_ENUM_ITEM_PPS, (ClsName, Prefix), __VA_ARGS__))  \
    MAKE_ENUM_ITEM_End(ClsName, Prefix);

附录

1. 检查 预处理器输出

​ 即使是vs2022默认的智能感知引擎也无法在hover tip上正确显示预处理的结果，所以需要手动用编译器展开观察中间结果

# MSVC	>> foreach_macro.i
while($true)
{
	cl /P foreach_macro.cpp
	sleep 1
}

# CLANG  >> stdout	(or append "-o foreach_macro.i")
while($true)
{
	clang -E foreach_macro.cpp
	sleep 1
}