mem_fun_ref
inline mem_fun_ref_t<_Ret,_Tp> mem_fun_ref(_Ret (_Tp::*__f)())
inline const_mem_fun_ref_t<_Ret,_Tp> mem_fun_ref(_Ret (_Tp::*__f)() const)
inline mem_fun1_ref_t<_Ret,_Tp,_Arg> mem_fun_ref(_Ret (_Tp::*__f)(_Arg))
mem_fun_ref(_Ret (_Tp::*__f)(_Arg) const)