nowide/detail/is_string_container.hpp

0001 //
0002 // Copyright (c) 2020 Alexander Grund
0003 //
0004 // Distributed under the Boost Software License, Version 1.0.
0005 // https://www.boost.org/LICENSE_1_0.txt
0006
0007 #ifndef BOOST_NOWIDE_DETAIL_IS_STRING_CONTAINER_HPP_INCLUDED
0008 #define BOOST_NOWIDE_DETAIL_IS_STRING_CONTAINER_HPP_INCLUDED
0009
0010 #include <cstddef>
0011 #include <type_traits>
0012
0013 namespace boost {
0014 namespace nowide {
0015     namespace detail {
0016         template<class...>
0017         struct make_void
0018         {
0019             typedef void type;
0020         };
0021
0022         template<class... Ts>
0023         using void_t = typename make_void<Ts...>::type;
0024
0025         template<typename T>
0026         struct is_char_type : std::false_type
0027         {};
0028         template<>
0029         struct is_char_type<char> : std::true_type
0030         {};
0031         template<>
0032         struct is_char_type<wchar_t> : std::true_type
0033         {};
0034         template<>
0035         struct is_char_type<char16_t> : std::true_type
0036         {};
0037         template<>
0038         struct is_char_type<char32_t> : std::true_type
0039         {};
0040 #ifdef __cpp_char8_t
0041         template<>
0042         struct is_char_type<char8_t> : std::true_type
0043         {};
0044 #endif
0045
0046         template<typename T>
0047         struct is_c_string : std::false_type
0048         {};
0049         template<typename T>
0050         struct is_c_string<const T*> : is_char_type<T>
0051         {};
0052
0053         template<typename T>
0054         using const_data_result = decltype(std::declval<const T>().data());
0055         /// Return the size of the char type returned by the data() member function
0056         template<typename T>
0057         using get_data_width =
0058           std::integral_constant<std::size_t, sizeof(typename std::remove_pointer<const_data_result<T>>::type)>;
0059         template<typename T>
0060         using size_result = decltype(std::declval<T>().size());
0061         /// Return true if the data() member function returns a pointer to a type of size 1
0062         template<typename T>
0063         using has_narrow_data = std::integral_constant<bool, (get_data_width<T>::value == 1)>;
0064
0065         /// Return true if T is a string container, e.g. std::basic_string, std::basic_string_view
0066         /// Requires a static value `npos`, a member function `size()` returning an integral,
0067         /// and a member function `data()` returning a C string
0068         template<typename T, bool isNarrow, typename = void>
0069         struct is_string_container : std::false_type
0070         {};
0071         // clang-format off
0072         template<typename T, bool isNarrow>
0073         struct is_string_container<T, isNarrow, void_t<decltype(T::npos), size_result<T>, const_data_result<T>>>
0074             : std::integral_constant<bool,
0075                                      std::is_integral<decltype(T::npos)>::value
0076                                        && std::is_integral<size_result<T>>::value
0077                                        && is_c_string<const_data_result<T>>::value
0078                                        && isNarrow == has_narrow_data<T>::value>
0079         {};
0080         // clang-format on
0081         template<typename T>
0082         using requires_narrow_string_container = typename std::enable_if<is_string_container<T, true>::value>::type;
0083         template<typename T>
0084         using requires_wide_string_container = typename std::enable_if<is_string_container<T, false>::value>::type;
0085
0086         template<typename T>
0087         using requires_narrow_char = typename std::enable_if<sizeof(T) == 1 && is_char_type<T>::value>::type;
0088         template<typename T>
0089         using requires_wide_char = typename std::enable_if<(sizeof(T) > 1) && is_char_type<T>::value>::type;
0090
0091     } // namespace detail
0092 } // namespace nowide
0093 } // namespace boost
0094
0095 #endif