From a7da4881303a7bc9a59014f0d03cd946a9cdecec Mon Sep 17 00:00:00 2001
From: Ville Voutilainen <ville.voutilainen@gmail.com>
Date: Wed, 30 Nov 2016 11:59:50 +0200
Subject: Implement LWG 2534, Constrain rvalue stream operators.

* include/std/istream (__is_convertible_to_basic_istream): New.
(__is_extractable): Likewise.
(operator>>(basic_istream<_CharT, _Traits>&&, _Tp&&)):
Turn the stream parameter into a template parameter
and constrain.
* include/std/ostream (__is_convertible_to_basic_ostream): New.
(__is_insertable): Likewise.
(operator<<(basic_ostream<_CharT, _Traits>&&, const _Tp&)):
Turn the stream parameter into a template parameter
and constrain.
* testsuite/27_io/basic_istream/extractors_other/char/4.cc: New.
* testsuite/27_io/basic_istream/extractors_other/wchar_t/4.cc:
Likewise.
* testsuite/27_io/basic_ostream/inserters_other/char/6.cc: Likewise.
* testsuite/27_io/basic_ostream/inserters_other/wchar_t/6.cc: Likewise.

From-SVN: r243006
---
 libstdc++-v3/include/std/istream | 33 ++++++++++++++++++++++++++++++---
 libstdc++-v3/include/std/ostream | 33 ++++++++++++++++++++++++++++++---
 2 files changed, 60 insertions(+), 6 deletions(-)

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

diff --git a/libstdc++-v3/include/std/istream b/libstdc++-v3/include/std/istream
index c8a2e08..4f0e940 100644
--- a/libstdc++-v3/include/std/istream
+++ b/libstdc++-v3/include/std/istream
@@ -908,6 +908,28 @@ _GLIBCXX_BEGIN_NAMESPACE_VERSION
     ws(basic_istream<_CharT, _Traits>& __is);
 
 #if __cplusplus >= 201103L
+
+  template<typename _Tp>
+    struct __is_convertible_to_basic_istream
+    {
+      template<typename _Ch, typename _Up>
+      static true_type __check(basic_istream<_Ch, _Up>*);
+
+      static false_type __check(void*);
+    public:
+      using type = decltype(__check(declval<_Tp*>()));
+      constexpr static bool value = type::value;
+  };
+
+  template<typename _Istream, typename _Tp, typename = void>
+    struct __is_extractable : false_type {};
+
+  template<typename _Istream, typename _Tp>
+    struct __is_extractable<_Istream, _Tp,
+			    __void_t<decltype(declval<_Istream&>()
+					      >> declval<_Tp>())>>
+    : true_type {};
+
   // [27.7.1.6] Rvalue stream extraction
   // _GLIBCXX_RESOLVE_LIB_DEFECTS
   // 2328. Rvalue stream extraction should use perfect forwarding
@@ -921,9 +943,14 @@ _GLIBCXX_BEGIN_NAMESPACE_VERSION
    *  rvalue streams since they won't bind to the extractor functions
    *  that take an lvalue reference.
   */
-  template<typename _CharT, typename _Traits, typename _Tp>
-    inline basic_istream<_CharT, _Traits>&
-    operator>>(basic_istream<_CharT, _Traits>&& __is, _Tp&& __x)
+  template<typename _Istream, typename _Tp>
+    inline
+    typename enable_if<__and_<__not_<is_lvalue_reference<_Istream>>,
+			      __is_convertible_to_basic_istream<
+				typename remove_reference<_Istream>::type>,
+			      __is_extractable<_Istream&, _Tp&&>>::value,
+		       _Istream&>::type
+    operator>>(_Istream&& __is, _Tp&& __x)
     {
       __is >> std::forward<_Tp>(__x);
       return __is;
diff --git a/libstdc++-v3/include/std/ostream b/libstdc++-v3/include/std/ostream
index 0bf53f0..a1fe892 100644
--- a/libstdc++-v3/include/std/ostream
+++ b/libstdc++-v3/include/std/ostream
@@ -613,6 +613,27 @@ _GLIBCXX_BEGIN_NAMESPACE_VERSION
     { return __os.flush(); }
 
 #if __cplusplus >= 201103L
+  template<typename _Tp>
+    struct __is_convertible_to_basic_ostream
+  {
+    template<typename _Ch, typename _Up>
+    static true_type __check(basic_ostream<_Ch, _Up>*);
+
+    static false_type __check(void*);
+  public:
+    using type = decltype(__check(declval<_Tp*>()));
+    constexpr static bool value = type::value;
+  };
+
+  template<typename _Ostream, typename _Tp, typename = void>
+    struct __is_insertable : false_type {};
+
+  template<typename _Ostream, typename _Tp>
+    struct __is_insertable<_Ostream, _Tp,
+			   __void_t<decltype(declval<_Ostream&>()
+					     << declval<const _Tp&>())>>
+				    : true_type {};
+
   /**
    *  @brief  Generic inserter for rvalue stream
    *  @param  __os  An input stream.
@@ -623,9 +644,15 @@ _GLIBCXX_BEGIN_NAMESPACE_VERSION
    *  rvalue streams since they won't bind to the inserter functions
    *  that take an lvalue reference.
   */
-  template<typename _CharT, typename _Traits, typename _Tp>
-    inline basic_ostream<_CharT, _Traits>&
-    operator<<(basic_ostream<_CharT, _Traits>&& __os, const _Tp& __x)
+  template<typename _Ostream, typename _Tp>
+    inline
+    typename enable_if<__and_<__not_<is_lvalue_reference<_Ostream>>,
+			      __is_convertible_to_basic_ostream<
+				typename remove_reference<_Ostream>::type>,
+			      __is_insertable<_Ostream&, const _Tp&>>::value,
+		       _Ostream&>::type
+				      //basic_ostream<_CharT, _Traits>&
+    operator<<(_Ostream&& __os, const _Tp& __x)
     {
       __os << __x;
       return __os;
-- 
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