Implement string_view from the library fundamentals TS (n4023). Also works in C++11 and 03, with reduced functionality (mostly in the area of constexpr)

git-svn-id: https://llvm.org/svn/llvm-project/libcxx/trunk@210659 91177308-0d34-0410-b5e6-96231b3b80d8

test/experimental/string.view/string.view.ops/basic_string.pass.cpp

@@ -0,0 +1,63 @@
+//===----------------------------------------------------------------------===//
+//
+//                     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>
+
+// template<class _Allocator>
+// explicit operator basic_string<_CharT, _Traits, _Allocator>() const
+
+#include <experimental/string_view>
+#include <cassert>
+
+template<typename CharT>
+void test ( const CharT *s ) {
+    typedef std::experimental::basic_string_view<CharT> string_view_t;
+    typedef std::basic_string<CharT> string_t;
+    
+    {
+    string_view_t sv1 ( s );
+    string_t      str = (string_t) sv1;
+
+    assert ( sv1.size() == str.size ());
+    assert ( std::char_traits<CharT>::compare ( sv1.data(), str.data(), sv1.size()) == 0 );
+    }
+
+    {
+    string_view_t sv1;
+    string_t      str = (string_t) sv1;
+
+    assert ( sv1.size() == str.size ());
+    assert ( std::char_traits<CharT>::compare ( sv1.data(), str.data(), sv1.size()) == 0 );
+    }
+}
+
+int main () {
+    test ( "ABCDEABCDEABCDEABCDEABCDEABCDEABCDEABCDEABCDEABCDEABCDEABCDEABCDEABCDEABCDEABCDEABCDEABCDEABCDEABCDEABCDE" );
+    test ( "ABCDE");
+    test ( "a" );
+    test ( "" );
+
+    test ( L"ABCDEABCDEABCDEABCDEABCDEABCDEABCDEABCDEABCDEABCDEABCDEABCDEABCDEABCDEABCDEABCDEABCDEABCDEABCDEABCDEABCDE" );
+    test ( L"ABCDE" );
+    test ( L"a" );
+    test ( L"" );
+
+#if __cplusplus >= 201103L
+    test ( u"ABCDEABCDEABCDEABCDEABCDEABCDEABCDEABCDEABCDEABCDEABCDEABCDEABCDEABCDEABCDEABCDEABCDEABCDEABCDEABCDEABCDE" );
+    test ( u"ABCDE" );
+    test ( u"a" );
+    test ( u"" );
+
+    test ( U"ABCDEABCDEABCDEABCDEABCDEABCDEABCDEABCDEABCDEABCDEABCDEABCDEABCDEABCDEABCDEABCDEABCDEABCDEABCDEABCDEABCDE" );
+    test ( U"ABCDE" );
+    test ( U"a" );
+    test ( U"" );
+#endif
+}