@@ -356,6 +356,13 @@ _GLIBCXX_BEGIN_NAMESPACE_VERSION
template <size_t _Idx>
in_place_tag in_place(__in_place_index<_Idx>*) {terminate();}
+#define __cpp_lib_as_const 201510
+ template<typename _Tp>
+ constexpr add_const_t<_Tp>& as_const(_Tp& __t) noexcept { return __t; }
+
+ template<typename _Tp>
+ void as_const(const _Tp&&) = delete;
+
#endif
_GLIBCXX_END_NAMESPACE_VERSION
new file mode 100644
@@ -0,0 +1,30 @@
+// Copyright (C) 2016 Free Software Foundation, Inc.
+//
+// This file is part of the GNU ISO C++ Library. This library is free
+// software; you can redistribute it and/or modify it under the
+// terms of the GNU General Public License as published by the
+// Free Software Foundation; either version 3, or (at your option)
+// any later version.
+
+// This library is distributed in the hope that it will be useful,
+// but WITHOUT ANY WARRANTY; without even the implied warranty of
+// MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
+// GNU General Public License for more details.
+
+// You should have received a copy of the GNU General Public License along
+// with this library; see the file COPYING3. If not see
+// <http://www.gnu.org/licenses/>.
+
+// { dg-options "-std=gnu++17" }
+// { dg-do compile }
+
+#include <utility>
+
+#if __cpp_lib_as_const != 201510
+# error "__cpp_lib_as_const != 201510"
+#endif
+
+int i;
+constexpr auto& ci = std::as_const(i);
+static_assert( &i == &ci );
+static_assert( std::is_same_v<decltype(std::as_const(i)), const int&> );
new file mode 100644
@@ -0,0 +1,28 @@
+// Copyright (C) 2016 Free Software Foundation, Inc.
+//
+// This file is part of the GNU ISO C++ Library. This library is free
+// software; you can redistribute it and/or modify it under the
+// terms of the GNU General Public License as published by the
+// Free Software Foundation; either version 3, or (at your option)
+// any later version.
+
+// This library is distributed in the hope that it will be useful,
+// but WITHOUT ANY WARRANTY; without even the implied warranty of
+// MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
+// GNU General Public License for more details.
+
+// You should have received a copy of the GNU General Public License along
+// with this library; see the file COPYING3. If not see
+// <http://www.gnu.org/licenses/>.
+
+// { dg-options "-std=gnu++17" }
+// { dg-do compile }
+
+#include <utility>
+
+void test01()
+{
+ int i = 0;
+ std::as_const(std::move(i)); // { dg-error "deleted function" }
+ std::as_const(0); // { dg-error "deleted function" }
+}