From 82e8c3da7408bc0695511ee13f88d451c8adadd8 Mon Sep 17 00:00:00 2001
From: Jonathan Wakely <jwakely@redhat.com>
Date: Tue, 23 Apr 2019 11:27:14 +0100
Subject: [PATCH] Corrections for C++2a std::unwrap_reference traits

The P0318R1 paper added to the C++2a draft recently was not the latest
version of the paper, and should have included these changes. These
changes will be made to the working draft via a Defect Report, so I'm
applying them to libstdc++ now.

	* include/std/type_traits (unwrap_reference_t): Define for C++2a.
	(unwrap_ref_decay): Remove inheritance from unwrap_reference.
	* testsuite/20_util/unwrap_reference/1.cc: Adjust test to use alias.

From-SVN: r270506
---
 libstdc++-v3/ChangeLog                               | 6 ++++++
 libstdc++-v3/include/std/type_traits                 | 5 ++++-
 libstdc++-v3/testsuite/20_util/unwrap_reference/1.cc | 2 +-
 3 files changed, 11 insertions(+), 2 deletions(-)

diff --git a/libstdc++-v3/ChangeLog b/libstdc++-v3/ChangeLog
index e222cb30de9..f04a7e009a5 100644
--- a/libstdc++-v3/ChangeLog
+++ b/libstdc++-v3/ChangeLog
@@ -1,3 +1,9 @@
+2019-04-23  Jonathan Wakely  <jwakely@redhat.com>
+
+	* include/std/type_traits (unwrap_reference_t): Define for C++2a.
+	(unwrap_ref_decay): Remove inheritance from unwrap_reference.
+	* testsuite/20_util/unwrap_reference/1.cc: Adjust test to use alias.
+
 2019-04-23  Ramana Radhakrishnan  <ramana.radhakrishnan@arm.com>
 	    Bernd Edlinger  <bernd.edlinger@hotmail.de>
 	    Jakub Jelinek  <jakub@redhat.com>
diff --git a/libstdc++-v3/include/std/type_traits b/libstdc++-v3/include/std/type_traits
index c3cb67a457d..e0ac5c88dfc 100644
--- a/libstdc++-v3/include/std/type_traits
+++ b/libstdc++-v3/include/std/type_traits
@@ -3067,9 +3067,12 @@ template <typename _From, typename _To>
   template<typename _Tp>
     struct unwrap_reference<reference_wrapper<_Tp>> { using type = _Tp&; };
 
+  template<typename _Tp>
+    using unwrap_reference_t = typename unwrap_reference<_Tp>::type;
+
   /// Decay type and if it's a reference_wrapper, unwrap it
   template<typename _Tp>
-    struct unwrap_ref_decay : unwrap_reference<decay_t<_Tp>> { };
+    struct unwrap_ref_decay { using type = unwrap_reference_t<decay_t<_Tp>>; };
 
   template<typename _Tp>
     using unwrap_ref_decay_t = typename unwrap_ref_decay<_Tp>::type;
diff --git a/libstdc++-v3/testsuite/20_util/unwrap_reference/1.cc b/libstdc++-v3/testsuite/20_util/unwrap_reference/1.cc
index 38feca4bb5b..243526725a0 100644
--- a/libstdc++-v3/testsuite/20_util/unwrap_reference/1.cc
+++ b/libstdc++-v3/testsuite/20_util/unwrap_reference/1.cc
@@ -28,7 +28,7 @@ template<typename T, typename U = T>
   {
     using std::unwrap_reference;
     using T2 = typename unwrap_reference<T>::type;
-    static_assert(expect_same<T2, typename unwrap_reference<T2>::type>::value);
+    static_assert(expect_same<T2, std::unwrap_reference_t<T2>>::value);
     return expect_same<T2, U>::value;
   }
 
-- 
2.30.2