Implement std::string_view as described in http://wg21.link/P0254R1. Reviewed as https://reviews.llvm.org/D21459

git-svn-id: https://llvm.org/svn/llvm-project/libcxx/trunk@276238 91177308-0d34-0410-b5e6-96231b3b80d8

test/std/strings/string.view/string.view.cons/default.pass.cpp

@@ -0,0 +1,46 @@
+//===----------------------------------------------------------------------===//
+//
+//                     The LLVM Compiler Infrastructure
+//
+// This file is dual licensed under the MIT and the University of Illinois Open
+// Source Licenses. See LICENSE.TXT for details.
+//
+//===----------------------------------------------------------------------===//
+
+
+// <string_view>
+
+// constexpr basic_string_view () noexcept;
+
+#include <string_view>
+#include <cassert>
+
+template<typename T>
+void test () {
+#if _LIBCPP_STD_VER > 11
+    {
+    constexpr T sv1;
+    static_assert ( sv1.size() == 0, "" );
+    static_assert ( sv1.empty(), "");
+    }
+#endif
+
+    {
+    T sv1;
+    assert ( sv1.size() == 0 );
+    assert ( sv1.empty());
+    }
+}
+
+int main () {
+    typedef std::string_view    string_view;
+    typedef std::u16string_view u16string_view;
+    typedef std::u32string_view u32string_view;
+    typedef std::wstring_view   wstring_view;
+
+    test<string_view> ();
+    test<u16string_view> ();
+    test<u32string_view> ();
+    test<wstring_view> ();
+
+}