From b271eff4c697ea278dc38088c95246b1c5a278e5 Mon Sep 17 00:00:00 2001
From: Howard Hinnant <hhinnant@apple.com>
Date: Wed, 11 Aug 2010 14:05:55 +0000
Subject: [PATCH] Modified the definition of std::foward to address National
 Body Comment US 90

git-svn-id: https://llvm.org/svn/llvm-project/libcxx/trunk@110805 91177308-0d34-0410-b5e6-96231b3b80d8
---
 include/type_traits | 46 +++++++++++++++++++++++++++++++++++++--------
 1 file changed, 38 insertions(+), 8 deletions(-)

diff --git a/include/type_traits b/include/type_traits
index fc144716..35777c8e 100644
--- a/include/type_traits
+++ b/include/type_traits
@@ -1140,20 +1140,50 @@ move(_Tp&& __t)
     return static_cast<typename remove_reference<_Tp>::type&&>(__t);
 }
 
-template <class _Tp, class _Up,
-    class = typename _STD::enable_if<
-         is_lvalue_reference<_Tp>::value ? is_lvalue_reference<_Up>::value : true
-                     >::type,
-    class = typename _STD::enable_if<
-         is_convertible<typename remove_reference<_Up>::type*,
-                        typename remove_reference<_Tp>::type*>::value>::type>
+template <class _Tp,
+          class = typename enable_if<
+                     !is_lvalue_reference<_Tp>::value
+                  >::type
+         >
 inline _LIBCPP_INLINE_VISIBILITY
 _Tp&&
-forward(_Up&& __t)
+forward(typename common_type<_Tp>::type& __t)
 {
     return static_cast<_Tp&&>(__t);
 }
 
+template <class _Tp,
+          class = typename enable_if<
+                     !is_lvalue_reference<_Tp>::value
+                  >::type
+         >
+inline _LIBCPP_INLINE_VISIBILITY
+_Tp&&
+forward(typename common_type<_Tp>::type&& __t)
+{
+    return static_cast<_Tp&&>(__t);
+}
+
+template <class _Tp,
+          class = typename enable_if<
+                     is_lvalue_reference<_Tp>::value
+                  >::type
+         >
+inline _LIBCPP_INLINE_VISIBILITY
+_Tp
+forward(typename common_type<_Tp>::type __t)
+{
+    return __t;
+}
+
+template <class _Tp,
+          class = typename enable_if<
+                     is_lvalue_reference<_Tp>::value
+                  >::type
+         >
+_Tp
+forward(typename remove_reference<_Tp>::type&& __t) = delete;
+
 #else  // _LIBCPP_MOVE
 
 template <class _Tp>