Check if a class has a member function of a given signature

Question

I\'m asking for a template trick to detect if a class has a specific member function of a given signature.

The problem is similar to the one cited here http://www.go

Answer 1

With c++ 20 this becomes much simpler. Say we want to test if a class T has a member function void T::resize(typename T::size_type). For example, std::vector has such a member function. Then,

template
concept has_resize_member_func = requires {
    typename T::size_type;
    { std::declval().resize(std::declval()) } -> std::same_as;
};

and the usage is

static_assert(has_resize_member_func, "");
static_assert(has_resize_member_func == false, "");