Revert r276548 - Make pair/tuples assignment operators SFINAE properly.

This is a breaking change. The SFINAE required is instantiated the second
the class is instantiated, and this can cause hard SFINAE errors
when applied to references to incomplete types. Ex.

struct IncompleteType;
extern IncompleteType it;
std::tuple<IncompleteType&> t(it); // SFINAE will blow up.

llvm-svn: 276598

1 files changed, 5 insertions, 20 deletions

diff --git a/libcxx/include/utility b/libcxx/include/utility
index 9a155a00fb4..022a641d6e8 100644
--- a/libcxx/include/utility
+++ b/libcxx/include/utility
@@ -348,19 +348,8 @@ struct _LIBCPP_TYPE_VIS_ONLY pair
   // Use the implicitly declared copy constructor in C++03
 #endif
 
-    typedef typename remove_reference<_T1>::type _T1Unref;
-    typedef typename remove_reference<_T2>::type _T2Unref;
-
-#if !defined(_LIBCPP_CXX03_LANG)
-    typedef integral_constant<bool,
-           is_copy_assignable<_T1>::value
-        && is_copy_assignable<_T2>::value> _CanCopyAssign;
-#else
-    typedef true_type _CanCopyAssign;
-#endif
-
     _LIBCPP_INLINE_VISIBILITY
-    pair& operator=(typename conditional<_CanCopyAssign::value, pair, __nat>::type const& __p)
+    pair& operator=(const pair& __p)
         _NOEXCEPT_(is_nothrow_copy_assignable<first_type>::value &&
                    is_nothrow_copy_assignable<second_type>::value)
     {
@@ -388,15 +377,10 @@ struct _LIBCPP_TYPE_VIS_ONLY pair
             : first(_VSTD::forward<_U1>(__p.first)),
               second(_VSTD::forward<_U2>(__p.second)) {}
 
-    typedef integral_constant<bool,
-           is_move_assignable<_T1>::value
-        && is_move_assignable<_T2>::value> _CanMoveAssign;
-
     _LIBCPP_INLINE_VISIBILITY
     pair&
-    operator=(typename conditional<_CanMoveAssign::value, pair, __nat>::type&& __p)
-        _NOEXCEPT_(is_nothrow_move_assignable<first_type>::value &&
-                   is_nothrow_move_assignable<second_type>::value)
+    operator=(pair&& __p) _NOEXCEPT_(is_nothrow_move_assignable<first_type>::value &&
+                                     is_nothrow_move_assignable<second_type>::value)
     {
         first = _VSTD::forward<first_type>(__p.first);
         second = _VSTD::forward<second_type>(__p.second);
@@ -404,6 +388,7 @@ struct _LIBCPP_TYPE_VIS_ONLY pair
     }
 
 #ifndef _LIBCPP_HAS_NO_VARIADICS
+
     template<class _Tuple,
              class = typename enable_if<__tuple_convertible<_Tuple, pair>::value>::type>
         _LIBCPP_INLINE_VISIBILITY _LIBCPP_CONSTEXPR_AFTER_CXX11
@@ -426,7 +411,7 @@ struct _LIBCPP_TYPE_VIS_ONLY pair
             {}
 
     template <class _Tuple,
-              class = typename enable_if<!is_same<typename decay<_Tuple>::type, pair>::value && __tuple_assignable<_Tuple, pair>::value>::type>
+              class = typename enable_if<__tuple_assignable<_Tuple, pair>::value>::type>
         _LIBCPP_INLINE_VISIBILITY
         pair&
         operator=(_Tuple&& __p)