SFINAE check if expression compiles and return std::true_type [duplicate]

Answer 1

I personally use that (which use full signature):

#include 

#define DEFINE_HAS_SIGNATURE(traitsName, funcName, signature)               \
    template                                  \
    class traitsName                                                        \
    {                                                                       \
    private:                                                                \
        template struct helper;                              \
        template                                                \
        static std::uint8_t check(helper*);           \
        template static std::uint16_t check(...);               \
    public:                                                                 \
        static                                                              \
        constexpr bool value = sizeof(check(0)) == sizeof(std::uint8_t); \
    }

So in your case, use something like:

DEFINE_HAS_SIGNATURE(has_func_name, T::func_name, void (T::*)(Args...));

And test it like:

struct C
{
    void func_name(char, int);
};

static_assert(has_func_name::value, "unexpected non declared void C::func_name(char, int)");
static_assert(!has_func_name::value, "unexpected declared void C::func_name(int, int)");