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cpp foreach macro

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showcase

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

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// 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. __Choose30th

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    #define __Choose30th(_1, _2, _3, _4, _5, _6, _7, _8, _9, _10,
                     _11, _12, _13, _14, _15, _16, _17, _18, _19, _20,
                     _21, _22, _23, _24, _25, _26, _27, _28, _29, _30,
                    ...) _30

  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, 当然msvc也支持相关选项切换到gcc like的宏展开行为

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

  3. Callx + CallxPPS

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    #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

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// clang-format off
#define __Choose30th(_1, _2, _3, _4, _5, _6, _7, _8, _9, _10,\
                     _11, _12, _13, _14, _15, _16, _17, _18, _19, _20,\
                     _21, _22, _23, _24, _25, _26, _27, _28, _29, _30,\
                    ...) _30
#define ID(_1, ...) _1
#define IDx(...) __VA_ARGS__
#define Callx(f, ...) ID(f(__VA_ARGS__))
#define CallxPPS(f, _1) ID(f _1)
#define FOREACH0(it_operator, pps, ...)
#define FOREACH1(it_operator, pps, _1, ...)  IDx(it_operator(pps, _1) FOREACH0 (it_operator, pps, __VA_ARGS__))
#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 FOREACH12(it_operator, pps, _1, ...) IDx(it_operator(pps, _1) FOREACH11(it_operator, pps, __VA_ARGS__))
#define FOREACH13(it_operator, pps, _1, ...) IDx(it_operator(pps, _1) FOREACH12(it_operator, pps, __VA_ARGS__))
#define FOREACH14(it_operator, pps, _1, ...) IDx(it_operator(pps, _1) FOREACH13(it_operator, pps, __VA_ARGS__))
#define FOREACH15(it_operator, pps, _1, ...) IDx(it_operator(pps, _1) FOREACH14(it_operator, pps, __VA_ARGS__))
#define FOREACH16(it_operator, pps, _1, ...) IDx(it_operator(pps, _1) FOREACH15(it_operator, pps, __VA_ARGS__))
#define FOREACH17(it_operator, pps, _1, ...) IDx(it_operator(pps, _1) FOREACH16(it_operator, pps, __VA_ARGS__))
#define FOREACH18(it_operator, pps, _1, ...) IDx(it_operator(pps, _1) FOREACH17(it_operator, pps, __VA_ARGS__))
#define FOREACH19(it_operator, pps, _1, ...) IDx(it_operator(pps, _1) FOREACH18(it_operator, pps, __VA_ARGS__))
#define FOREACH20(it_operator, pps, _1, ...) IDx(it_operator(pps, _1) FOREACH19(it_operator, pps, __VA_ARGS__))
#define FOREACH21(it_operator, pps, _1, ...) IDx(it_operator(pps, _1) FOREACH20(it_operator, pps, __VA_ARGS__))
#define FOREACH22(it_operator, pps, _1, ...) IDx(it_operator(pps, _1) FOREACH21(it_operator, pps, __VA_ARGS__))
#define FOREACH23(it_operator, pps, _1, ...) IDx(it_operator(pps, _1) FOREACH22(it_operator, pps, __VA_ARGS__))
#define FOREACH24(it_operator, pps, _1, ...) IDx(it_operator(pps, _1) FOREACH23(it_operator, pps, __VA_ARGS__))
#define FOREACH25(it_operator, pps, _1, ...) IDx(it_operator(pps, _1) FOREACH24(it_operator, pps, __VA_ARGS__))
#define FOREACH26(it_operator, pps, _1, ...) IDx(it_operator(pps, _1) FOREACH25(it_operator, pps, __VA_ARGS__))
#define FOREACH27(it_operator, pps, _1, ...) IDx(it_operator(pps, _1) FOREACH26(it_operator, pps, __VA_ARGS__))
#define FOREACH28(it_operator, pps, _1, ...) IDx(it_operator(pps, _1) FOREACH27(it_operator, pps, __VA_ARGS__))
// clang-format on
#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
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#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
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#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可能无法在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

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# 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
}