const_mem_fun1_ref_t

template<class Result, class Ty, class Arg>
    struct const_mem_fun1_ref_t
        : public binary_function<Ty, Arg, Result> {
    explicit const_mem_fun1_ref_t(Result (Ty::*pm)(Arg) const);
    Result operator()(const Ty& left, Arg right) const;
    };

The template class stores a copy of pm, which must be a pointer to a member function of class Ty, in a private member object. It defines its member function operator() as returning (left.*pm)(right) const.