PR libstdc++/83830 Define std::has_unique_object_representations_v

	PR libstdc++/83830
	* include/std/type_traits (has_unique_object_representations_v): Add
	variable template.
	* testsuite/20_util/has_unique_object_representations/value.cc: Check
	variable template.

From-SVN: r256701

libstdc++-v3/ChangeLog

+2018-01-15  Jonathan Wakely  <jwakely@redhat.com>
+
+	PR libstdc++/83830
+	* include/std/type_traits (has_unique_object_representations_v): Add
+	variable template.
+	* testsuite/20_util/has_unique_object_representations/value.cc: Check
+	variable template.
+
 2018-01-15  Ville Voutilainen  <ville.voutilainen@gmail.com>
 
 	Make optional conditionally

libstdc++-v3/include/std/type_traits

@@ -2903,6 +2903,10 @@ template <typename _From, typename _To>
       remove_cv_t<remove_all_extents_t<_Tp>>
       )>
     { };
+
+  template<typename _Tp>
+    inline constexpr bool has_unique_object_representations_v
+      = has_unique_object_representations<_Tp>::value;
 #endif
 #undef _GLIBCXX_HAVE_BUILTIN_HAS_UNIQ_OBJ_REP
 

libstdc++-v3/testsuite/20_util/has_unique_object_representations/value.cc

@@ -108,3 +108,17 @@ void test01()
   static_assert(test_category<has_unique_object_representations,
 		Aligned[][1]>(false), "");
 }
+
+void
+test02()
+{
+  using std::has_unique_object_representations;
+  using std::has_unique_object_representations_v;
+
+  static_assert(has_unique_object_representations_v<int>
+		== has_unique_object_representations<int>::value);
+  static_assert(has_unique_object_representations_v<void>
+		== has_unique_object_representations<void>::value);
+  static_assert(has_unique_object_representations_v<float>
+		== has_unique_object_representations<float>::value);
+}