将constness添加到函数指针时会发生什么？

Question

Static assertions all fail. What type is Constifier creating for a function pointer?

#include <type_traits>

template<typename T>
struct Constifier;

template<typename T>
struct Constifier<T *>
{
    typedef const T *Type;
};

int main()
{
    static_assert(std::is_same<typename Constifier<int (*)()>::Type, const int (*)()>::value, "");
    static_assert(std::is_same<typename Constifier<int (*)()>::Type, int (*const)()>::value, "");
    static_assert(std::is_same<typename Constifier<int (*)()>::Type, void>::value, "");
}

Answer 1

The function pointer is unchanged:

static_assert(std::is_same<typename Constifier<int (*)()>::Type, int (*)()>::value, "");

You cannot alter a function because it lives in the code section of the memory, so you can think of a function pointer implicity pointing to const already.