Perfect forwarding a member of object

Question

Suppose I have two structs:

struct X {};
struct Y { X x; }

I have functions:

void f(X&);
void f(X&&         


        

Answer 1

template <typename T>
void g(T&& t) {
  f(std::forward<T>(t).x);
}

Answer 2

I think this will work, although I'm not sure:

template<class T, class M>
struct mforward {
  using type = M&&; 
};
template<class T, class M>
struct mforward<T&, M> {
  using type = M&; 
};

template <typename T>
void g(T&& t) {
  f(std::forward<typename mforward<T, decltype(t.x)>::type>(t.x));
}