| Line | Branch | Exec | Source |
|---|---|---|---|
| 1 | // | ||
| 2 | // Copyright (c) 2025 Vinnie Falco (vinnie dot falco at gmail dot com) | ||
| 3 | // | ||
| 4 | // Distributed under the Boost Software License, Version 1.0. (See accompanying | ||
| 5 | // file LICENSE_1_0.txt or copy at http://www.boost.org/LICENSE_1_0.txt) | ||
| 6 | // | ||
| 7 | // Official repository: https://github.com/cppalliance/capy | ||
| 8 | // | ||
| 9 | |||
| 10 | #ifndef BOOST_CAPY_TYPE_TRAITS_HPP | ||
| 11 | #define BOOST_CAPY_TYPE_TRAITS_HPP | ||
| 12 | |||
| 13 | #include <boost/capy/detail/config.hpp> | ||
| 14 | |||
| 15 | #include <concepts> | ||
| 16 | #include <cstddef> | ||
| 17 | #include <tuple> | ||
| 18 | #include <type_traits> | ||
| 19 | #include <utility> | ||
| 20 | |||
| 21 | namespace boost { | ||
| 22 | namespace capy { | ||
| 23 | |||
| 24 | /** Concept for types that support the tuple protocol. | ||
| 25 | |||
| 26 | A type satisfies `has_tuple_protocol` if `std::tuple_size<T>` | ||
| 27 | is a complete type with a `value` member. | ||
| 28 | |||
| 29 | @tparam T The type to check. | ||
| 30 | */ | ||
| 31 | template<typename T> | ||
| 32 | concept has_tuple_protocol = requires { | ||
| 33 | std::tuple_size<std::remove_cvref_t<T>>::value; | ||
| 34 | }; | ||
| 35 | |||
| 36 | namespace detail { | ||
| 37 | |||
| 38 | template<typename T, std::size_t... Is> | ||
| 39 | auto decomposed_types_impl(std::index_sequence<Is...>) | ||
| 40 | -> std::tuple<std::tuple_element_t<Is, std::remove_cvref_t<T>>...>; | ||
| 41 | |||
| 42 | template<typename T> | ||
| 43 | requires has_tuple_protocol<T> | ||
| 44 | using decomposed_types_t = decltype( | ||
| 45 | decomposed_types_impl<T>( | ||
| 46 | std::make_index_sequence<std::tuple_size_v<std::remove_cvref_t<T>>>{} | ||
| 47 | ) | ||
| 48 | ); | ||
| 49 | |||
| 50 | template<typename T> | ||
| 51 | ✗ | auto get_awaiter(T&& t) | |
| 52 | { | ||
| 53 | if constexpr (requires { std::forward<T>(t).operator co_await(); }) | ||
| 54 | { | ||
| 55 | return std::forward<T>(t).operator co_await(); | ||
| 56 | } | ||
| 57 | else if constexpr (requires { operator co_await(std::forward<T>(t)); }) | ||
| 58 | { | ||
| 59 | return operator co_await(std::forward<T>(t)); | ||
| 60 | } | ||
| 61 | else | ||
| 62 | { | ||
| 63 | ✗ | return std::forward<T>(t); | |
| 64 | } | ||
| 65 | } | ||
| 66 | |||
| 67 | template<typename A> | ||
| 68 | using awaitable_return_t = decltype( | ||
| 69 | get_awaiter(std::declval<A>()).await_resume() | ||
| 70 | ); | ||
| 71 | |||
| 72 | } // namespace detail | ||
| 73 | |||
| 74 | /** Concept for types that decompose to a specific typelist. | ||
| 75 | |||
| 76 | A type satisfies `decomposes_to` if it supports structured bindings | ||
| 77 | via the tuple protocol and its element types match the specified | ||
| 78 | typelist exactly. | ||
| 79 | |||
| 80 | @tparam T The type to check. | ||
| 81 | @tparam Types The expected element types after decomposition. | ||
| 82 | |||
| 83 | @par Requirements | ||
| 84 | @li `T` must satisfy the tuple protocol (`std::tuple_size`, | ||
| 85 | `std::tuple_element`) | ||
| 86 | @li The number of elements must equal `sizeof...(Types)` | ||
| 87 | @li Each element type must match the corresponding type in `Types` | ||
| 88 | |||
| 89 | @par Example | ||
| 90 | @code | ||
| 91 | static_assert(decomposes_to<std::pair<int, double>, int, double>); | ||
| 92 | static_assert(decomposes_to<std::tuple<int, float, char>, int, float, char>); | ||
| 93 | static_assert(decomposes_to<std::array<int, 3>, int, int, int>); | ||
| 94 | |||
| 95 | // Constrain a function template | ||
| 96 | template<typename T> | ||
| 97 | requires decomposes_to<T, system::error_code, std::size_t> | ||
| 98 | void process_result(T&& result) | ||
| 99 | { | ||
| 100 | auto [ec, n] = std::forward<T>(result); | ||
| 101 | // ... | ||
| 102 | } | ||
| 103 | @endcode | ||
| 104 | |||
| 105 | @note Plain aggregates without the tuple protocol are not supported. | ||
| 106 | Use `std::pair`, `std::tuple`, `std::array`, or add the tuple | ||
| 107 | protocol to your type. | ||
| 108 | */ | ||
| 109 | template<typename T, typename... Types> | ||
| 110 | concept decomposes_to = | ||
| 111 | has_tuple_protocol<T> && | ||
| 112 | std::same_as< | ||
| 113 | detail::decomposed_types_t<T>, | ||
| 114 | std::tuple<Types...> | ||
| 115 | >; | ||
| 116 | |||
| 117 | /** Concept for awaitables whose return type decomposes to a specific typelist. | ||
| 118 | |||
| 119 | A type satisfies `awaitable_decomposes_to` if it is an awaitable | ||
| 120 | (has `await_resume`) and its return type satisfies @ref decomposes_to | ||
| 121 | with the specified typelist. | ||
| 122 | |||
| 123 | @tparam A The awaitable type. | ||
| 124 | @tparam Types The expected element types after decomposition. | ||
| 125 | |||
| 126 | @par Requirements | ||
| 127 | @li `A` must be an awaitable (directly or via `operator co_await`) | ||
| 128 | @li The return type of `await_resume()` must satisfy @ref decomposes_to | ||
| 129 | with `Types...` | ||
| 130 | |||
| 131 | @par Example | ||
| 132 | @code | ||
| 133 | // Constrain a function to accept only awaitables that return | ||
| 134 | // a decomposable result of (error_code, size_t) | ||
| 135 | template<typename A> | ||
| 136 | requires awaitable_decomposes_to<A, system::error_code, std::size_t> | ||
| 137 | task<void> process(A&& op) | ||
| 138 | { | ||
| 139 | auto [ec, n] = co_await std::forward<A>(op); | ||
| 140 | if (ec) | ||
| 141 | co_return; | ||
| 142 | // process n bytes... | ||
| 143 | } | ||
| 144 | @endcode | ||
| 145 | |||
| 146 | @see decomposes_to | ||
| 147 | */ | ||
| 148 | template<typename A, typename... Types> | ||
| 149 | concept awaitable_decomposes_to = requires { | ||
| 150 | typename detail::awaitable_return_t<A>; | ||
| 151 | } && decomposes_to<detail::awaitable_return_t<A>, Types...>; | ||
| 152 | |||
| 153 | } // namespace capy | ||
| 154 | } // namespace boost | ||
| 155 | |||
| 156 | #endif | ||
| 157 |