// // Copyright (c) 2020 Alexander Grund // // Distributed under the Boost Software License, Version 1.0. (See // accompanying file LICENSE or copy at // http://www.boost.org/LICENSE_1_0.txt) // #ifndef BOOST_NOWIDE_DETAIL_IS_STRING_CONTAINER_HPP_INCLUDED #define BOOST_NOWIDE_DETAIL_IS_STRING_CONTAINER_HPP_INCLUDED #include <cstddef> #include <type_traits> namespace boost { namespace nowide { namespace detail { template<class...> struct make_void { typedef void type; }; template<class... Ts> using void_t = typename make_void<Ts...>::type; template<typename T> struct is_char_type : std::false_type {}; template<> struct is_char_type<char> : std::true_type {}; template<> struct is_char_type<wchar_t> : std::true_type {}; template<> struct is_char_type<char16_t> : std::true_type {}; template<> struct is_char_type<char32_t> : std::true_type {}; #ifdef __cpp_char8_t template<> struct is_char_type<char8_t> : std::true_type {}; #endif template<typename T> struct is_c_string : std::false_type {}; template<typename T> struct is_c_string<const T*> : is_char_type<T> {}; template<typename T> using const_data_result = decltype(std::declval<const T>().data()); /// Return the size of the char type returned by the data() member function template<typename T> using get_data_width = std::integral_constant<std::size_t, sizeof(typename std::remove_pointer<const_data_result<T>>::type)>; template<typename T> using size_result = decltype(std::declval<T>().size()); /// Return true if the data() member function returns a pointer to a type of size 1 template<typename T> using has_narrow_data = std::integral_constant<bool, (get_data_width<T>::value == 1)>; /// Return true if T is a string container, e.g. std::basic_string, std::basic_string_view /// Requires a static value `npos`, a member function `size()` returning an integral, /// and a member function `data()` returning a C string template<typename T, bool isNarrow, typename = void> struct is_string_container : std::false_type {}; // clang-format off template<typename T, bool isNarrow> struct is_string_container<T, isNarrow, void_t<decltype(T::npos), size_result<T>, const_data_result<T>>> : std::integral_constant<bool, std::is_integral<decltype(T::npos)>::value && std::is_integral<size_result<T>>::value && is_c_string<const_data_result<T>>::value && isNarrow == has_narrow_data<T>::value> {}; // clang-format on template<typename T> using requires_narrow_string_container = typename std::enable_if<is_string_container<T, true>::value>::type; template<typename T> using requires_wide_string_container = typename std::enable_if<is_string_container<T, false>::value>::type; template<typename T> using requires_narrow_char = typename std::enable_if<sizeof(T) == 1 && is_char_type<T>::value>::type; template<typename T> using requires_wide_char = typename std::enable_if<(sizeof(T) > 1) && is_char_type<T>::value>::type; } // namespace detail } // namespace nowide } // namespace boost #endif