Defined in header <functional> template< class R, class T >
/*unspecified*/ mem_fn(R T::* pm); (1) (since C++11) template< class R, class T, class... Args >
/*unspecified*/ mem_fn(R (T::* pm)(Args...));
template< class R, class T, class... Args >
/*unspecified*/ mem_fn(R (T::* pm)(Args...) const);
template< class R, class T, class... Args >
/*unspecified*/ mem_fn(R (T::* pm)(Args...) volatile);
template< class R, class T, class... Args >
/*un