libstdc++/68877 Reimplement std::__is_swappable

2016-01-12  Daniel Kruegler  <daniel.kruegler@gmail.com>

	PR libstdc++/68877
	* include/std/type_traits: Following N4511, reimplement __is_swappable
	and __is_nothrow_swappable. Move __is_swappable to namespace std,
	adjust callers. Use __is_nothrow_swappable in swap.
	* include/bits/move.h: Use __is_nothrow_swappable in swap.
	* testsuite/20_util/is_nothrow_swappable/value.cc: Extend; remove
	__is_swappable related tests.
	* testsuite/20_util/is_swappable/value.cc: New.
	* testsuite/20_util/is_swappable/requirements/
	explicit_instantiation.cc: New.
	* testsuite/20_util/is_swappable/requirements/typedefs.cc: New.
	* testsuite/25_algorithms/swap/68877.cc: New.

git-svn-id: svn+ssh://gcc.gnu.org/svn/gcc/trunk@232296 138bc75d-0d04-0410-961f-82ee72b054a4

2 files changed, 47 insertions, 23 deletions

diff --git a/libstdc++-v3/include/bits/move.h b/libstdc++-v3/include/bits/move.h
index a9bcdca37c1..afcea2d8468 100644
--- a/libstdc++-v3/include/bits/move.h
+++ b/libstdc++-v3/include/bits/move.h
@@ -198,9 +198,9 @@ _GLIBCXX_BEGIN_NAMESPACE_VERSION
   template<typename _Tp, size_t _Nm>
     inline
 #if __cplusplus >= 201103L
-    typename enable_if<__is_swappable_impl::__is_swappable<_Tp>::value>::type
+    typename enable_if<__is_swappable<_Tp>::value>::type
     swap(_Tp (&__a)[_Nm], _Tp (&__b)[_Nm])
-    noexcept(noexcept(swap(*__a, *__b)))
+    noexcept(__is_nothrow_swappable<_Tp>::value)
 #else
     void
     swap(_Tp (&__a)[_Nm], _Tp (&__b)[_Nm])
diff --git a/libstdc++-v3/include/std/type_traits b/libstdc++-v3/include/std/type_traits
index 37f039bcfe1..3a2b546b22f 100644
--- a/libstdc++-v3/include/std/type_traits
+++ b/libstdc++-v3/include/std/type_traits
@@ -2587,12 +2587,11 @@ _GLIBCXX_BEGIN_NAMESPACE_VERSION
     : true_type								\
     { };
 
+  template <typename _Tp>
+    struct __is_swappable;
 
-   namespace __is_swappable_impl {
-     template <typename _Tp, typename=void>
-     struct __is_swappable : public false_type
-     { };
-   }
+  template <typename _Tp>
+    struct __is_nothrow_swappable;
 
   template<typename _Tp>
     inline
@@ -2604,33 +2603,58 @@ _GLIBCXX_BEGIN_NAMESPACE_VERSION
 
   template<typename _Tp, size_t _Nm>
     inline
-    typename enable_if<__is_swappable_impl::__is_swappable<_Tp>::value>::type
+    typename enable_if<__is_swappable<_Tp>::value>::type
     swap(_Tp (&__a)[_Nm], _Tp (&__b)[_Nm])
-    noexcept(noexcept(swap(*__a, *__b)));
+    noexcept(__is_nothrow_swappable<_Tp>::value);
 
-  namespace __is_swappable_impl {
+  namespace __swappable_details {
     using std::swap;
 
-    template <typename _Tp>
-    struct __is_swappable<_Tp, __void_t<decltype(swap(declval<_Tp&>(),
-                                                      declval<_Tp&>()))>>
-    : public true_type
-    { };
+    struct __do_is_swappable_impl
+    {
+      template<typename _Tp, typename
+               = decltype(swap(std::declval<_Tp&>(), std::declval<_Tp&>()))>
+        static true_type __test(int);
+
+      template<typename>
+        static false_type __test(...);
+    };
+
+    struct __do_is_nothrow_swappable_impl
+    {
+      template<typename _Tp>
+        static __bool_constant<
+          noexcept(swap(std::declval<_Tp&>(), std::declval<_Tp&>()))
+        > __test(int);
+
+      template<typename>
+        static false_type __test(...);
+    };
+
   }
 
-  template <bool, typename _Tp>
+  template<typename _Tp>
+    struct __is_swappable_impl
+    : public __swappable_details::__do_is_swappable_impl
+    {
+      typedef decltype(__test<_Tp>(0)) type;
+    };
+
+  template<typename _Tp>
     struct __is_nothrow_swappable_impl
-    : public __bool_constant<noexcept(swap(declval<_Tp&>(), declval<_Tp&>()))>
-    { };
+    : public __swappable_details::__do_is_nothrow_swappable_impl
+    {
+      typedef decltype(__test<_Tp>(0)) type;
+    };
 
-  template <typename _Tp>
-    struct __is_nothrow_swappable_impl<false, _Tp> : public false_type
+  template<typename _Tp>
+    struct __is_swappable
+    : public __is_swappable_impl<_Tp>::type
     { };
 
-  template <typename _Tp>
+  template<typename _Tp>
     struct __is_nothrow_swappable
-    : public __is_nothrow_swappable_impl<
-               __is_swappable_impl::__is_swappable<_Tp>::value, _Tp>
+    : public __is_nothrow_swappable_impl<_Tp>::type
     { };
 
 _GLIBCXX_END_NAMESPACE_VERSION