整理

include/boost/nowide/detail/is_path.hpp

@@ -0,0 +1,38 @@
+//
+// Copyright (c) 2020 Alexander Grund
+//
+// Distributed under the Boost Software License, Version 1.0.
+// https://www.boost.org/LICENSE_1_0.txt
+
+#ifndef BOOST_NOWIDE_DETAIL_IS_PATH_HPP_INCLUDED
+#define BOOST_NOWIDE_DETAIL_IS_PATH_HPP_INCLUDED
+
+#include <type_traits>
+
+namespace boost {
+namespace nowide {
+    namespace detail {
+
+        /// Trait to heuristically check for a *\::filesystem::path
+        /// Done by checking for make_preferred and filename member functions with correct signature
+        template<typename T>
+        struct is_path
+        {
+            template<typename U, U& (U::*)(), U (U::*)() const>
+            struct Check;
+            template<typename U>
+            static std::true_type test(Check<U, &U::make_preferred, &U::filename>*);
+            template<typename U>
+            static std::false_type test(...);
+
+            static constexpr bool value = decltype(test<T>(0))::value;
+        };
+        /// SFINAE trait/alias which resolves to Result if the Path is a *\::filesystem::path
+        template<typename Path, typename Result>
+        using enable_if_path_t = typename std::enable_if<is_path<Path>::value, Result>::type;
+
+    } // namespace detail
+} // namespace nowide
+} // namespace boost
+
+#endif