如何将多参数模板传递给宏?

2022-01-11 00:00:00 macros templates c++

假设我有一个这样的宏:

Say I have a macro like this:

#define SET_TYPE_NAME(TYPE, NAME) 
    template<typename T>          
    std::string name();           
                                  
    template<>                    
    std::string name<TYPE>() {    
        return NAME;              
    }

如果我传递一个具有多个参数的模板，这将不起作用，因为 <int, int> 中的逗号被解释为分隔 宏 参数，而不是模板参数.

This won't work if I pass it a template that has more than one parameter, because the comma in the <int, int> is interpreted as separating the macro arguments, not the template arguments. 

SET_TYPE_NAME(std::map<int, int>, "TheMap")
// Error: macro expects two arguments, three given

这个问题似乎可以通过这样做来解决:

This problem seems to be solved by doing this:

SET_TYPE_NAME((std::map<int, int>), "TheMap")

但是现在又出现了一个问题，我真的没想到:

But now another problem arises, one that I really did not expect:

 template<>
 std::string name<(std::map<int, int>)>()
 // template argument 1 is invalid

似乎多余的括号使模板参数无效.有没有办法解决这个问题?

It seems that the extra parentheses make the template argument invalid. Is there any way around this?

推荐答案

除了typedef，你可以切换参数的顺序和使用可变参数宏(需要C99或C++11兼容的编译器):

Besides typedef, you could switch the order of the arguments and use variadic macros (requires C99 or C++11-compatible compiler):

#define SET_TYPE_NAME(NAME, ...) 
template<typename T>          
std::string name();           
                              
template<>                    
std::string name<__VA_ARGS__>() {    
    return NAME;              
}

...

SET_TYPE_NAME("TheMap", std::map<int, int>)

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