| 1 | // |
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| 2 | // uses_executor.hpp |
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| 3 | // ~~~~~~~~~~~~~~~~~ |
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| 4 | // |
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| 5 | // Copyright (c) 2003-2024 Christopher M. Kohlhoff (chris at kohlhoff dot com) |
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| 6 | // |
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| 7 | // Distributed under the Boost Software License, Version 1.0. (See accompanying |
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| 8 | // file LICENSE_1_0.txt or copy at http://www.boost.org/LICENSE_1_0.txt) |
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| 9 | // |
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| 10 | |
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| 11 | #ifndef BOOST_ASIO_USES_EXECUTOR_HPP |
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| 12 | #define BOOST_ASIO_USES_EXECUTOR_HPP |
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| 13 | |
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| 14 | #if defined(_MSC_VER) && (_MSC_VER >= 1200) |
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| 15 | # pragma once |
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| 16 | #endif // defined(_MSC_VER) && (_MSC_VER >= 1200) |
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| 17 | |
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| 18 | #include <boost/asio/detail/config.hpp> |
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| 19 | #include <boost/asio/detail/type_traits.hpp> |
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| 20 | |
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| 21 | #include <boost/asio/detail/push_options.hpp> |
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| 22 | |
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| 23 | namespace boost { |
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| 24 | namespace asio { |
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| 25 | |
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| 26 | /// A special type, similar to std::nothrow_t, used to disambiguate |
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| 27 | /// constructors that accept executor arguments. |
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| 28 | /** |
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| 29 | * The executor_arg_t struct is an empty structure type used as a unique type |
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| 30 | * to disambiguate constructor and function overloading. Specifically, some |
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| 31 | * types have constructors with executor_arg_t as the first argument, |
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| 32 | * immediately followed by an argument of a type that satisfies the Executor |
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| 33 | * type requirements. |
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| 34 | */ |
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| 35 | struct executor_arg_t |
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| 36 | { |
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| 37 | /// Constructor. |
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| 38 | constexpr executor_arg_t() noexcept |
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| 39 | { |
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| 40 | } |
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| 41 | }; |
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| 42 | |
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| 43 | /// A special value, similar to std::nothrow, used to disambiguate constructors |
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| 44 | /// that accept executor arguments. |
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| 45 | /** |
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| 46 | * See boost::asio::executor_arg_t and boost::asio::uses_executor |
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| 47 | * for more information. |
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| 48 | */ |
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| 49 | constexpr executor_arg_t executor_arg; |
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| 50 | |
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| 51 | /// The uses_executor trait detects whether a type T has an associated executor |
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| 52 | /// that is convertible from type Executor. |
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| 53 | /** |
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| 54 | * Meets the BinaryTypeTrait requirements. The Asio library provides a |
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| 55 | * definition that is derived from false_type. A program may specialize this |
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| 56 | * template to derive from true_type for a user-defined type T that can be |
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| 57 | * constructed with an executor, where the first argument of a constructor has |
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| 58 | * type executor_arg_t and the second argument is convertible from type |
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| 59 | * Executor. |
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| 60 | */ |
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| 61 | template <typename T, typename Executor> |
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| 62 | struct uses_executor : false_type {}; |
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| 63 | |
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| 64 | } // namespace asio |
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| 65 | } // namespace boost |
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| 66 | |
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| 67 | #include <boost/asio/detail/pop_options.hpp> |
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| 68 | |
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| 69 | #endif // BOOST_ASIO_USES_EXECUTOR_HPP |
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| 70 | |
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