C++ 11/14：如何從類型中刪除指向成員的指針？

Question

在C++ 11或C++ 1Y/14：給定指針到構件型的形式T C::*的值我想獲得被指向的型T.

例如：

#include <iostream> 
using namespace std; 

struct T1 { static void f() { cout << "T1" << endl; } }; 
struct T2 { static void f() { cout << "T2" << endl; } }; 

struct U1 { T1 x; }; 
struct U2 { T2 x; }; 

template<class C> struct V; 
template<> struct V<U1> { static constexpr T1 U1::* pm = &U1::x; }; 
template<> struct V<U2> { static constexpr T2 U2::* pm = &U2::x; }; 

template<class W> 
void f(W pm) 
{ 
    typedef ??? T; 
    T::f(); 
} 

int main() 
{ 
     f(V<U1>::pm); 
     f(V<U2>::pm); 
} 

有沒有辦法做到這一點？上面的???是什麼？

更新：

這裏是的libstdc的消毒版本++實現的std::remove_pointer：

template<typename T, typename> 
struct remove_pointer_helper 
{ 
    typedef T type; 
}; 

template<typename T, typename U> 
struct remove_pointer_helper<T, U*> 
{ 
    typedef U type; 
}; 

template<typename T> 
struct remove_pointer 
    : public remove_pointer_helper<T, typename remove_cv<T>::type> 
{}; 

更新2：

這裏是最終的解決方案，謝謝：

#include <iostream> 
using namespace std; 

template<typename T, typename> 
struct remove_member_pointer_helper 
{ 
    typedef T type; 
}; 

template<typename T, typename U, typename C> 
struct remove_member_pointer_helper<T, U C::*> 
{ 
    typedef U type; 
}; 

template<typename T> 
struct remove_member_pointer 
    : public remove_member_pointer_helper<T, typename remove_cv<T>::type> 
{}; 

template<typename T> 
using remove_member_pointer_t = typename remove_member_pointer<T>::type; 

struct T1 { static void f() { cout << "T1" << endl; } }; 
struct T2 { static void f() { cout << "T2" << endl; } }; 

struct U1 { T1 x; }; 
struct U2 { T2 x; }; 

template<class C> 
struct V; 

template<> struct V<U1> { static constexpr T1 U1::* pm = &U1::x; }; 
template<> struct V<U2> { static constexpr T2 U2::* pm = &U2::x; }; 

template<class W> 
void f(W pm) 
{ 
     remove_member_pointer_t<W>::f(); 
} 

int main() 
{ 
     f(V<U1>::pm); 
     f(V<U2>::pm); 
} 

Answer 1

這其實是一種簡單的鍛鍊模板特殊化：

template<class T> struct remove_member_pointer { 
    typedef T type; 
}; 
template<class C, class T> struct remove_member_pointer<T C::*> { 
    typedef T type; 
};