c++ - 用于定义带有公开模板参数的模板结构的宏

Question

是否可以创建一个宏来减少仅公开其所有模板参数的模板结构定义的样板文件？

template <
    typename TPar1,
    int TPar2,
    ...
    bool TParN
>
struct MyStruct {
    using Par1 = TPar1;
    static int const Par2 = TPar2;
    ...
    static bool const ParN = TParN;
};

注意模板参数类型的不规则映射(typename->using, TYPE->static TYPE const).我也会对无法自动映射这些类型的解决方案感到满意，但例如仅支持类型名或需要提示是类型名还是类型。

Answer 1

我找到了解决办法。一些功劳归功于this answer用于计算传递的参数数量。

#define  GET_1(p1, ...) p1
#define  GET_2(p1, p2, ...) p2
#define  GET_3(p1, p2, p3, ...) p3
#define  GET_4(p1, p2, p3, p4, ...) p4
#define  GET_5(p1, p2, p3, p4, p5, ...) p5
#define  GET_6(p1, p2, p3, p4, p5, p6, ...) p6
#define  GET_7(p1, p2, p3, p4, p5, p6, p7, ...) p7
#define  GET_8(p1, p2, p3, p4, p5, p6, p7, p8, ...) p8
#define  GET_9(p1, p2, p3, p4, p5, p6, p7, p8, p9, ...) p9
#define GET_10(p1, p2, p3, p4, p5, p6, p7, p8, p9, p10, ...) p10
#define GET_11(p1, p2, p3, p4, p5, p6, p7, p8, p9, p10, p11, ...) p11
#define GET_12(p1, p2, p3, p4, p5, p6, p7, p8, p9, p10, p11, p12, ...) p12

#define  MAP_1(f, del, pars)                                 f( GET_1 pars)
#define  MAP_2(f, del, pars)  MAP_1(f, del, pars) del(dummy) f( GET_2 pars)
#define  MAP_3(f, del, pars)  MAP_2(f, del, pars) del(dummy) f( GET_3 pars)
#define  MAP_4(f, del, pars)  MAP_3(f, del, pars) del(dummy) f( GET_4 pars)
#define  MAP_5(f, del, pars)  MAP_4(f, del, pars) del(dummy) f( GET_5 pars)
#define  MAP_6(f, del, pars)  MAP_5(f, del, pars) del(dummy) f( GET_6 pars)
#define  MAP_7(f, del, pars)  MAP_6(f, del, pars) del(dummy) f( GET_7 pars)
#define  MAP_8(f, del, pars)  MAP_7(f, del, pars) del(dummy) f( GET_8 pars)
#define  MAP_9(f, del, pars)  MAP_8(f, del, pars) del(dummy) f( GET_9 pars)
#define MAP_10(f, del, pars)  MAP_9(f, del, pars) del(dummy) f(GET_10 pars)
#define MAP_11(f, del, pars) MAP_10(f, del, pars) del(dummy) f(GET_11 pars)
#define MAP_12(f, del, pars) MAP_11(f, del, pars) del(dummy) f(GET_12 pars)

#define CONCAT_HELPER(x, y) x##y
#define CONCAT(x, y) CONCAT_HELPER(x, y)

#define MAP(f, del, pars) CONCAT(MAP_, NUM_TUPLE_ARGS(pars))(f, del, pars)

#define NUM_MACRO_ARGS(...) NUM_MACRO_ARGS_HELPER1(__VA_ARGS__, 12, 11, 10, 9, 8, 7, 6, 5, 4, 3, 2, 1, 0)
#define NUM_MACRO_ARGS_HELPER1(...) NUM_MACRO_ARGS_HELPER2(__VA_ARGS__)
#define NUM_MACRO_ARGS_HELPER2(_1, _2, _3, _4, _5, _6, _7, _8, _9, _10, _11, _12, N, ...) N

#define NUM_TUPLE_ARGS(tuple) NUM_MACRO_ARGS tuple

#define GET_ARG_PAR_NAME(par_type, decl_type, name) T##name

#define MAKE_TEMPLATE_PART_VA(...) GET_1(__VA_ARGS__) GET_ARG_PAR_NAME(__VA_ARGS__)
#define MAKE_TEMPLATE_PART(param_def) MAKE_TEMPLATE_PART_VA param_def

#define MAKE_STRUCT_PART_VA(...) GET_2(__VA_ARGS__) GET_3(__VA_ARGS__) = GET_ARG_PAR_NAME(__VA_ARGS__);
#define MAKE_STRUCT_PART(param_def) MAKE_STRUCT_PART_VA param_def

#define TYPE_ARG(name) (typename, using, name)
#define VALUE_ARG(type, name) (type, static type const, name)

#define DELIMITER_TEMPLATE_PART(dummy) ,
#define DELIMITER_STRUCT_PART(dummy)

#define DEFINE_ALIAS_STRUCT(name, pars) template < MAP(MAKE_TEMPLATE_PART, DELIMITER_TEMPLATE_PART, pars) > struct name { MAP(MAKE_STRUCT_PART, DELIMITER_STRUCT_PART, pars) };

DEFINE_ALIAS_STRUCT(MyStruct3, (
    TYPE_ARG(Par1),
    VALUE_ARG(bool, Par2),
    TYPE_ARG(Par3),
    TYPE_ARG(Par4),
    TYPE_ARG(Par5),
    TYPE_ARG(Par6),
    TYPE_ARG(Par7),
    TYPE_ARG(Par8),
    TYPE_ARG(Par9)
))

这个例子扩展为:

template <
    typename TPar1,
    bool TPar2,
    typename TPar3,
    typename TPar4,
    typename TPar5,
    typename TPar6,
    typename TPar7,
    typename TPar8,
    typename TPar9
>
struct MyStruct3 {
    using Par1 = TPar1;
    static bool const Par2 = TPar2;
    using Par3 = TPar3;
    using Par4 = TPar4;
    using Par5 = TPar5;
    using Par6 = TPar6;
    using Par7 = TPar7;
    using Par8 = TPar8;
    using Par9 = TPar9;
};