LWG 2328 Rvalue stream extraction should use perfect forwarding

	* include/std/istream (operator>>(basic_istream&&, _Tp&)): Adjust
	to use perfect forwarding (LWG 2328).
	* testsuite/27_io/rvalue_streams.cc: Test perfect forwarding.
	* doc/xml/manual/intro.xml: Document DR 2328 status.

From-SVN: r238533

diff --git a/libstdc++-v3/ChangeLog b/libstdc++-v3/ChangeLog
index 40caba1..ad31fe6 100644 (file)
--- a/libstdc++-v3/ChangeLog
+++ b/libstdc++-v3/ChangeLog
@@ -1,5 +1,10 @@
 2016-07-20  Jonathan Wakely  <jwakely@redhat.com>
 
+       * include/std/istream (operator>>(basic_istream&&, _Tp&)): Adjust
+       to use perfect forwarding (LWG 2328).
+       * testsuite/27_io/rvalue_streams.cc: Test perfect forwarding.
+       * doc/xml/manual/intro.xml: Document DR 2328 status.
+
        * libsupc++/pbase_type_info.cc (__pbase_type_info::__do_catch): Use
        static objects for catching nullptr as pointer to member types.
 

diff --git a/libstdc++-v3/doc/xml/manual/intro.xml b/libstdc++-v3/doc/xml/manual/intro.xml
index 7b836cd..6335614 100644 (file)
--- a/libstdc++-v3/doc/xml/manual/intro.xml
+++ b/libstdc++-v3/doc/xml/manual/intro.xml
@@ -948,6 +948,12 @@ requirements of the license of GCC.
     <listitem><para>Update definitions of the partial specializations for const and volatile types.
     </para></listitem></varlistentry>
 
+    <varlistentry><term><link xmlns:xlink="http://www.w3.org/1999/xlink" xlink:href="../ext/lwg-defects.html#2328">2328</link>:
+       <emphasis>Rvalue stream extraction should use perfect forwarding</emphasis>
+    </term>
+    <listitem><para>Use perfect forwarding for right operand.
+    </para></listitem></varlistentry>
+
     <varlistentry><term><link xmlns:xlink="http://www.w3.org/1999/xlink" xlink:href="../ext/lwg-defects.html#2329">2329</link>:
        <emphasis><code>regex_match()/regex_search()</code> with <code>match_results</code> should forbid temporary strings</emphasis>
     </term>

diff --git a/libstdc++-v3/include/std/istream b/libstdc++-v3/include/std/istream
index d4cf7bc..c8a2e08 100644 (file)
--- a/libstdc++-v3/include/std/istream
+++ b/libstdc++-v3/include/std/istream
@@ -909,6 +909,8 @@ _GLIBCXX_BEGIN_NAMESPACE_VERSION
 
 #if __cplusplus >= 201103L
   // [27.7.1.6] Rvalue stream extraction
+  // _GLIBCXX_RESOLVE_LIB_DEFECTS
+  // 2328. Rvalue stream extraction should use perfect forwarding
   /**
    *  @brief  Generic extractor for rvalue stream
    *  @param  __is  An input stream.
@@ -921,9 +923,9 @@ _GLIBCXX_BEGIN_NAMESPACE_VERSION
   */
   template<typename _CharT, typename _Traits, typename _Tp>
     inline basic_istream<_CharT, _Traits>&
-    operator>>(basic_istream<_CharT, _Traits>&& __is, _Tp& __x)
+    operator>>(basic_istream<_CharT, _Traits>&& __is, _Tp&& __x)
     {
-      __is >> __x;
+      __is >> std::forward<_Tp>(__x);
       return __is;
     }
 #endif // C++11

diff --git a/libstdc++-v3/testsuite/27_io/rvalue_streams.cc b/libstdc++-v3/testsuite/27_io/rvalue_streams.cc
index eba5bc3..5918595 100644 (file)
--- a/libstdc++-v3/testsuite/27_io/rvalue_streams.cc
+++ b/libstdc++-v3/testsuite/27_io/rvalue_streams.cc
@@ -34,9 +34,33 @@ test01()
   VERIFY (i == i2);
 }
 
+struct X { bool as_rvalue; };
+
+void operator>>(std::istream&, X& x) { x.as_rvalue = false; }
+void operator>>(std::istream&, X&& x) { x.as_rvalue = true; }
+
+// LWG 2328 Rvalue stream extraction should use perfect forwarding
+void
+test02()
+{
+  X x;
+  std::istringstream is;
+  auto& ref1 = (std::move(is) >> x);
+  VERIFY( &ref1 == &is );
+  VERIFY( x.as_rvalue == false );
+  auto& ref2 = (std::move(is) >> std::move(x));
+  VERIFY( &ref2 == &is );
+  VERIFY( x.as_rvalue == true );
+
+  char arr[2];
+  std::istringstream("x") >> &arr[0];
+  std::istringstream("x") >> arr;
+}
+
 int
 main()
 {
   test01();
+  test02();
   return 0;
 }