A function adaptor for a template member references.
template<class S, class T> mem_fun_ref_t<S,T>
mem_fun_ref(S (T::*f)(A));
template<class S, class T, class A> mem_fun1_ref_t<S, T, A>
mem_fun_ref(S (T::*f)(A));
The template function mem_fun_ref returns an object through which X::f can be called given a reference to an X followed by the argument required for f.