[PATCH] Finish implementing "Treating Unnecessary decay" (P0777R1)

[Jonathan Wakely]

Some more recent-ish changes to the C++ working draft

        * include/std/tuple (apply): Use remove_reference_t instead of decay_t
        as per P0777R1.
        * include/std/type_traits (__result_of_memfun): Use remove_reference
        instead of __remove_cvref_t and remove redundant is_same check.
        (__inv_unwrap): Use __remove_cvref_t instead of decay_t.

Tested powerpc64le-linux, committed to trunk.


commit 1880e0a8be25f674c281db95e0224121a4a58201
Author: Jonathan Wakely <jwak...@redhat.com>
Date:   Wed Apr 24 17:03:52 2019 +0100

    Finish implementing "Treating Unnecessary decay" (P0777R1)
    
            * include/std/tuple (apply): Use remove_reference_t instead of 
decay_t
            as per P0777R1.
            * include/std/type_traits (__result_of_memfun): Use remove_reference
            instead of __remove_cvref_t and remove redundant is_same check.
            (__inv_unwrap): Use __remove_cvref_t instead of decay_t.

diff --git a/libstdc++-v3/include/std/tuple b/libstdc++-v3/include/std/tuple
index 0adef1ab384..6c7d91b7987 100644
--- a/libstdc++-v3/include/std/tuple
+++ b/libstdc++-v3/include/std/tuple
@@ -1674,7 +1674,7 @@ _GLIBCXX_BEGIN_NAMESPACE_VERSION
         second(std::forward<_Args2>(std::get<_Indexes2>(__tuple2))...)
       { }
 
-#if __cplusplus > 201402L
+#if __cplusplus >= 201703L
 # define __cpp_lib_apply 201603
 
   template <typename _Fn, typename _Tuple, size_t... _Idx>
@@ -1689,7 +1689,8 @@ _GLIBCXX_BEGIN_NAMESPACE_VERSION
     constexpr decltype(auto)
     apply(_Fn&& __f, _Tuple&& __t)
     {
-      using _Indices = make_index_sequence<tuple_size_v<decay_t<_Tuple>>>;
+      using _Indices
+       = make_index_sequence<tuple_size_v<remove_reference_t<_Tuple>>>;
       return std::__apply_impl(std::forward<_Fn>(__f),
                               std::forward<_Tuple>(__t),
                               _Indices{});
diff --git a/libstdc++-v3/include/std/type_traits 
b/libstdc++-v3/include/std/type_traits
index e0ac5c88dfc..1d14c751cfa 100644
--- a/libstdc++-v3/include/std/type_traits
+++ b/libstdc++-v3/include/std/type_traits
@@ -2327,10 +2327,9 @@ _GLIBCXX_BEGIN_NAMESPACE_VERSION
   template<typename _Res, typename _Class, typename _Arg, typename... _Args>
     struct __result_of_memfun<_Res _Class::*, _Arg, _Args...>
     {
-      typedef __remove_cvref_t<_Arg> _Argval;
+      typedef typename remove_reference<_Arg>::type _Argval;
       typedef _Res _Class::* _MemPtr;
-      typedef typename conditional<__or_<is_same<_Argval, _Class>,
-        is_base_of<_Class, _Argval>>::value,
+      typedef typename conditional<is_base_of<_Class, _Argval>::value,
         __result_of_memfun_ref<_MemPtr, _Arg, _Args...>,
         __result_of_memfun_deref<_MemPtr, _Arg, _Args...>
       >::type::type type;
@@ -2341,7 +2340,7 @@ _GLIBCXX_BEGIN_NAMESPACE_VERSION
   //        as the object expression
 
   // Used by result_of, invoke etc. to unwrap a reference_wrapper.
-  template<typename _Tp, typename _Up = typename decay<_Tp>::type>
+  template<typename _Tp, typename _Up = __remove_cvref_t<_Tp>>
     struct __inv_unwrap
     {
       using type = _Tp;