Функции-члены с "ref-qualifier"

#include <iostream>
#include <type_traits>
 
 
int main() {
   struct dummy {
      
      void one() {}
 
      void two() & {}
 
      void three() && {}
   };
 
   std::cout << std::boolalpha;
   std::cout << std::is_member_function_pointer<decltype(&dummy::one)>::value << std::endl;
   std::cout << std::is_member_function_pointer<decltype(&dummy::two)>::value << std::endl;
   std::cout << std::is_member_function_pointer<decltype(&dummy::three)>::value << std::endl;
}

template<typename>
    struct __is_member_function_pointer_helper
    : public false_type { };
 
  template<typename _Tp, typename _Cp>
    struct __is_member_function_pointer_helper<_Tp _Cp::*>
    : public integral_constant<bool, is_function<_Tp>::value> { };
 
  /// is_member_function_pointer
  template<typename _Tp>
    struct is_member_function_pointer
    : public integral_constant<bool, (__is_member_function_pointer_helper<
                      typename remove_cv<_Tp>::type>::value)>
    { };

#include <iostream>
#include <type_traits>
 
struct dummy {
      
      void one() { std::cout << "one\n"; }
 
      void two() & { std::cout << "two\n"; }
 
      void three() && { std::cout << "tree\n"; }
   }; 
 
namespace std {
 
template<typename _Res, typename... _ArgTypes>
    struct is_function<_Res(_ArgTypes...)&&>
    : public true_type { };
}
 
int main() {
   std::cout << std::boolalpha
             << std::is_member_function_pointer<decltype(&dummy::three)>::value 
             << std::endl;
}