Introduce new 'string_view' to match the one in the standard. Step #2 (up next) is to retire string_ref in favor of string_view

include/boost/utility/string_view_fwd.hpp

@@ -0,0 +1,39 @@
+/*
+   Copyright (c) Marshall Clow 2012-2012.
+
+   Distributed under the Boost Software License, Version 1.0. (See accompanying
+   file LICENSE_1_0.txt or copy at http://www.boost.org/LICENSE_1_0.txt)
+
+    For more information, see http://www.boost.org
+
+    Based on the StringRef implementation in LLVM (http://llvm.org) and
+    N3422 by Jeffrey Yasskin
+        http://www.open-std.org/jtc1/sc22/wg21/docs/papers/2012/n3442.html
+    Updated July 2015 to reflect the Library Fundamentals TS
+        http://www.open-std.org/jtc1/sc22/wg21/docs/papers/2015/n4480.html
+
+*/
+
+#ifndef BOOST_STRING_VIEW_FWD_HPP
+#define BOOST_STRING_VIEW_FWD_HPP
+
+#include <boost/config.hpp>
+#include <string>
+
+namespace boost {
+
+    template<typename charT, typename traits = std::char_traits<charT> > class basic_string_view;
+    typedef basic_string_view<char,     std::char_traits<char> >        string_view;
+    typedef basic_string_view<wchar_t,  std::char_traits<wchar_t> >    wstring_view;
+
+#ifndef BOOST_NO_CXX11_CHAR16_T
+    typedef basic_string_view<char16_t, std::char_traits<char16_t> > u16string_view;
+#endif
+
+#ifndef BOOST_NO_CXX11_CHAR32_T
+    typedef basic_string_view<char32_t, std::char_traits<char32_t> > u32string_view;
+#endif
+
+}
+
+#endif