From 5e88d2d08d464d80bbe5dfd64db954f2dd516b7e Mon Sep 17 00:00:00 2001
From: Ville Voutilainen <ville.voutilainen@gmail.com>
Date: Wed, 21 Jun 2017 22:53:26 +0300
Subject: PR libstdc++/80675, PR libstdc++/80940

* include/std/istream:
(__is_convertible_to_basic_istream_test(basic_istream<_Ch, _Up>*)): New.
(__do_is_convertible_to_basic_istream_impl): Likewise.
(__is_convertible_to_basic_istream_impl): Likewise.
(__is_convertible_to_basic_istream): Use the new base.
(__rvalue_istream_type): New.
(operator>>(_Istream&&, _Tp&&)): Use the new helper alias
for the SFINAE check, convert to the helper alias type before
doing the actual extraction.
* include/std/ostream:
(__is_convertible_to_basic_ostream_test(basic_ostream<_Ch, _Up>*)): New.
(__do_is_convertible_to_basic_ostream_impl): Likewise.
(__is_convertible_to_basic_ostream_impl): Likewise.
(__is_convertible_to_basic_ostream): Use the new base.
(__rvalue_ostream_type): New.
(operator<<(_Ostream&&, const _Tp&)): Use the new helper alias
for the SFINAE check, convert to the helper alias type before
doing the actual insertion.
* testsuite/27_io/rvalue_streams-2.cc: Add new tests.

From-SVN: r249468
---
 libstdc++-v3/include/std/istream | 52 ++++++++++++++++++++++++++++++----------
 1 file changed, 39 insertions(+), 13 deletions(-)

(limited to 'libstdc++-v3/include/std/istream')

diff --git a/libstdc++-v3/include/std/istream b/libstdc++-v3/include/std/istream
index 85c0a5a..1fa2555 100644
--- a/libstdc++-v3/include/std/istream
+++ b/libstdc++-v3/include/std/istream
@@ -908,20 +908,39 @@ _GLIBCXX_BEGIN_NAMESPACE_VERSION
     ws(basic_istream<_CharT, _Traits>& __is);
 
 #if __cplusplus >= 201103L
+  template<typename _Ch, typename _Up>
+    basic_istream<_Ch, _Up>&
+    __is_convertible_to_basic_istream_test(basic_istream<_Ch, _Up>*);
+
+  template<typename _Tp, typename = void>
+    struct __is_convertible_to_basic_istream_impl
+    {
+      using __istream_type = void;
+    };
 
   template<typename _Tp>
-    struct __is_convertible_to_basic_istream
+    using __do_is_convertible_to_basic_istream_impl =
+    decltype(__is_convertible_to_basic_istream_test
+	     (declval<typename remove_reference<_Tp>::type*>()));
+
+  template<typename _Tp>
+    struct __is_convertible_to_basic_istream_impl
+    <_Tp,
+     __void_t<__do_is_convertible_to_basic_istream_impl<_Tp>>>
     {
-      template<typename _Ch, typename _Up>
-      static basic_istream<_Ch, _Up>& __check(basic_istream<_Ch, _Up>*);
+      using __istream_type =
+	__do_is_convertible_to_basic_istream_impl<_Tp>;
+    };
 
-      static void __check(...);
+  template<typename _Tp>
+    struct __is_convertible_to_basic_istream
+    : __is_convertible_to_basic_istream_impl<_Tp>
+    {
     public:
-      using istream_type =
-	decltype(__check(declval<typename remove_reference<_Tp>::type*>()));
-      using type = __not_<is_same<istream_type, void>>;
+      using type = __not_<is_void<
+        typename __is_convertible_to_basic_istream_impl<_Tp>::__istream_type>>;
       constexpr static bool value = type::value;
-  };
+    };
 
   template<typename _Istream, typename _Tp, typename = void>
     struct __is_extractable : false_type {};
@@ -932,6 +951,11 @@ _GLIBCXX_BEGIN_NAMESPACE_VERSION
 					      >> declval<_Tp>())>>
     : true_type {};
 
+  template<typename _Istream>
+    using __rvalue_istream_type =
+      typename __is_convertible_to_basic_istream<
+	_Istream>::__istream_type;
+
   // [27.7.1.6] Rvalue stream extraction
   // _GLIBCXX_RESOLVE_LIB_DEFECTS
   // 2328. Rvalue stream extraction should use perfect forwarding
@@ -949,13 +973,15 @@ _GLIBCXX_BEGIN_NAMESPACE_VERSION
     inline
     typename enable_if<__and_<__not_<is_lvalue_reference<_Istream>>,
 			      __is_convertible_to_basic_istream<_Istream>,
-			      __is_extractable<_Istream&, _Tp&&>>::value,
-		       typename __is_convertible_to_basic_istream<
-			 _Istream>::istream_type>::type
+			      __is_extractable<
+				__rvalue_istream_type<_Istream>,
+				_Tp&&>>::value,
+		       __rvalue_istream_type<_Istream>>::type
     operator>>(_Istream&& __is, _Tp&& __x)
     {
-      __is >> std::forward<_Tp>(__x);
-      return __is;
+      __rvalue_istream_type<_Istream> __ret_is = __is;
+      __ret_is >> std::forward<_Tp>(__x);
+      return __ret_is;
     }
 #endif // C++11
 
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