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.io/stream_insert.pass.cpp

@@ -0,0 +1,58 @@
+//===----------------------------------------------------------------------===//
+//
+//                     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>
+
+// template<class charT, class traits, class Allocator>
+//   basic_ostream<charT, traits>&
+//   operator<<(basic_ostream<charT, traits>& os,
+//              const basic_string_view<charT,traits> str);
+
+#include <string_view>
+#include <sstream>
+#include <cassert>
+
+using std::string_view;
+using std::wstring_view;
+
+int main()
+{
+    {
+        std::ostringstream out;
+        string_view sv("some text");
+        out << sv;
+        assert(out.good());
+        assert(sv == out.str());
+    }
+    {
+        std::ostringstream out;
+        std::string s("some text");
+        string_view sv(s);
+        out.width(12);
+        out << sv;
+        assert(out.good());
+        assert("   " + s == out.str());
+    }
+    {
+        std::wostringstream out;
+        wstring_view sv(L"some text");
+        out << sv;
+        assert(out.good());
+        assert(sv == out.str());
+    }
+    {
+        std::wostringstream out;
+        std::wstring s(L"some text");
+        wstring_view sv(s);
+        out.width(12);
+        out << sv;
+        assert(out.good());
+        assert(L"   " + s == out.str());
+    }
+}