basic_string<Ch> optimization was implemented.

Author: ww898

include/ww898/utf_converters.hpp

@@ -584,12 +584,20 @@ Oit conv(std::basic_string_view<Ch> const & str, Oit && oit)
 
 template<
     typename Och,
-    typename Str>
+    typename Str,
+    typename std::enable_if<!std::is_same<typename std::decay<Str>::type, std::basic_string<Och>>::value, void *>::type = nullptr>
 std::basic_string<Och> conv(Str && str)
 {
     std::basic_string<Och> res;
     conv<utf_selector_t<Och>>(std::forward<Str>(str), std::back_inserter(res));
     return res;
 }
 
+template<
+    typename Ch>
+std::basic_string<Ch> conv(std::basic_string<Ch> str) noexcept
+{
+    return str;
+}
+
 }}

test/utf_converters_test.cpp

@@ -23,8 +23,10 @@
  */
 
 #if defined(_WIN32)
+#if !defined(_SILENCE_CXX17_CODECVT_HEADER_DEPRECATION_WARNING)
 #define _SILENCE_CXX17_CODECVT_HEADER_DEPRECATION_WARNING
 #endif
+#endif
 
 #include <ww898/utf_converters.hpp>
 
@@ -913,6 +915,7 @@ BOOST_AUTO_TEST_CASE(example, WW898_PERFORMANCE_TESTS_MODE)
     std::wstring uw;
     conv<utf8, utfw>(u8s, u8s + sizeof(u8s), std::back_inserter(uw));
     auto u8r = conv<char>(uw);
+    auto u16r = conv<char16_t>(u16);
     auto uwr = convz<wchar_t>(u8s);
 
 #if __cpp_lib_string_view >= 201606