| // |
| // execution/start.hpp |
| // ~~~~~~~~~~~~~~~~~~~ |
| // |
| // Copyright (c) 2003-2021 Christopher M. Kohlhoff (chris at kohlhoff dot com) |
| // |
| // Distributed under the Boost Software License, Version 1.0. (See accompanying |
| // file LICENSE_1_0.txt or copy at http://www.boost.org/LICENSE_1_0.txt) |
| // |
| |
| #ifndef BOOST_ASIO_EXECUTION_START_HPP |
| #define BOOST_ASIO_EXECUTION_START_HPP |
| |
| #if defined(_MSC_VER) && (_MSC_VER >= 1200) |
| # pragma once |
| #endif // defined(_MSC_VER) && (_MSC_VER >= 1200) |
| |
| #include <boost/asio/detail/config.hpp> |
| #include <boost/asio/detail/type_traits.hpp> |
| #include <boost/asio/traits/start_member.hpp> |
| #include <boost/asio/traits/start_free.hpp> |
| |
| #include <boost/asio/detail/push_options.hpp> |
| |
| #if defined(GENERATING_DOCUMENTATION) |
| |
| namespace boost { |
| namespace asio { |
| namespace execution { |
| |
| /// A customisation point that notifies an operation state object to start |
| /// its associated operation. |
| /** |
| * The name <tt>execution::start</tt> denotes a customisation point object. |
| * The expression <tt>execution::start(R)</tt> for some subexpression |
| * <tt>R</tt> is expression-equivalent to: |
| * |
| * @li <tt>R.start()</tt>, if that expression is valid. |
| * |
| * @li Otherwise, <tt>start(R)</tt>, if that expression is valid, with |
| * overload resolution performed in a context that includes the declaration |
| * <tt>void start();</tt> and that does not include a declaration of |
| * <tt>execution::start</tt>. |
| * |
| * @li Otherwise, <tt>execution::start(R)</tt> is ill-formed. |
| */ |
| inline constexpr unspecified start = unspecified; |
| |
| /// A type trait that determines whether a @c start expression is |
| /// well-formed. |
| /** |
| * Class template @c can_start is a trait that is derived from |
| * @c true_type if the expression <tt>execution::start(std::declval<R>(), |
| * std::declval<E>())</tt> is well formed; otherwise @c false_type. |
| */ |
| template <typename R> |
| struct can_start : |
| integral_constant<bool, automatically_determined> |
| { |
| }; |
| |
| } // namespace execution |
| } // namespace asio |
| } // namespace boost |
| |
| #else // defined(GENERATING_DOCUMENTATION) |
| |
| namespace asio_execution_start_fn { |
| |
| using boost::asio::decay; |
| using boost::asio::declval; |
| using boost::asio::enable_if; |
| using boost::asio::traits::start_free; |
| using boost::asio::traits::start_member; |
| |
| void start(); |
| |
| enum overload_type |
| { |
| call_member, |
| call_free, |
| ill_formed |
| }; |
| |
| template <typename R, typename = void, typename = void> |
| struct call_traits |
| { |
| BOOST_ASIO_STATIC_CONSTEXPR(overload_type, overload = ill_formed); |
| BOOST_ASIO_STATIC_CONSTEXPR(bool, is_noexcept = false); |
| typedef void result_type; |
| }; |
| |
| template <typename R> |
| struct call_traits<R, |
| typename enable_if< |
| start_member<R>::is_valid |
| >::type> : |
| start_member<R> |
| { |
| BOOST_ASIO_STATIC_CONSTEXPR(overload_type, overload = call_member); |
| }; |
| |
| template <typename R> |
| struct call_traits<R, |
| typename enable_if< |
| !start_member<R>::is_valid |
| >::type, |
| typename enable_if< |
| start_free<R>::is_valid |
| >::type> : |
| start_free<R> |
| { |
| BOOST_ASIO_STATIC_CONSTEXPR(overload_type, overload = call_free); |
| }; |
| |
| struct impl |
| { |
| #if defined(BOOST_ASIO_HAS_MOVE) |
| template <typename R> |
| BOOST_ASIO_CONSTEXPR typename enable_if< |
| call_traits<R>::overload == call_member, |
| typename call_traits<R>::result_type |
| >::type |
| operator()(R&& r) const |
| BOOST_ASIO_NOEXCEPT_IF(( |
| call_traits<R>::is_noexcept)) |
| { |
| return BOOST_ASIO_MOVE_CAST(R)(r).start(); |
| } |
| |
| template <typename R> |
| BOOST_ASIO_CONSTEXPR typename enable_if< |
| call_traits<R>::overload == call_free, |
| typename call_traits<R>::result_type |
| >::type |
| operator()(R&& r) const |
| BOOST_ASIO_NOEXCEPT_IF(( |
| call_traits<R>::is_noexcept)) |
| { |
| return start(BOOST_ASIO_MOVE_CAST(R)(r)); |
| } |
| #else // defined(BOOST_ASIO_HAS_MOVE) |
| template <typename R> |
| BOOST_ASIO_CONSTEXPR typename enable_if< |
| call_traits<R&>::overload == call_member, |
| typename call_traits<R&>::result_type |
| >::type |
| operator()(R& r) const |
| BOOST_ASIO_NOEXCEPT_IF(( |
| call_traits<R&>::is_noexcept)) |
| { |
| return r.start(); |
| } |
| |
| template <typename R> |
| BOOST_ASIO_CONSTEXPR typename enable_if< |
| call_traits<const R&>::overload == call_member, |
| typename call_traits<const R&>::result_type |
| >::type |
| operator()(const R& r) const |
| BOOST_ASIO_NOEXCEPT_IF(( |
| call_traits<const R&>::is_noexcept)) |
| { |
| return r.start(); |
| } |
| |
| template <typename R> |
| BOOST_ASIO_CONSTEXPR typename enable_if< |
| call_traits<R&>::overload == call_free, |
| typename call_traits<R&>::result_type |
| >::type |
| operator()(R& r) const |
| BOOST_ASIO_NOEXCEPT_IF(( |
| call_traits<R&>::is_noexcept)) |
| { |
| return start(r); |
| } |
| |
| template <typename R> |
| BOOST_ASIO_CONSTEXPR typename enable_if< |
| call_traits<const R&>::overload == call_free, |
| typename call_traits<const R&>::result_type |
| >::type |
| operator()(const R& r) const |
| BOOST_ASIO_NOEXCEPT_IF(( |
| call_traits<const R&>::is_noexcept)) |
| { |
| return start(r); |
| } |
| #endif // defined(BOOST_ASIO_HAS_MOVE) |
| }; |
| |
| template <typename T = impl> |
| struct static_instance |
| { |
| static const T instance; |
| }; |
| |
| template <typename T> |
| const T static_instance<T>::instance = {}; |
| |
| } // namespace asio_execution_start_fn |
| namespace boost { |
| namespace asio { |
| namespace execution { |
| namespace { |
| |
| static BOOST_ASIO_CONSTEXPR const asio_execution_start_fn::impl& |
| start = asio_execution_start_fn::static_instance<>::instance; |
| |
| } // namespace |
| |
| template <typename R> |
| struct can_start : |
| integral_constant<bool, |
| asio_execution_start_fn::call_traits<R>::overload != |
| asio_execution_start_fn::ill_formed> |
| { |
| }; |
| |
| #if defined(BOOST_ASIO_HAS_VARIABLE_TEMPLATES) |
| |
| template <typename R> |
| constexpr bool can_start_v = can_start<R>::value; |
| |
| #endif // defined(BOOST_ASIO_HAS_VARIABLE_TEMPLATES) |
| |
| template <typename R> |
| struct is_nothrow_start : |
| integral_constant<bool, |
| asio_execution_start_fn::call_traits<R>::is_noexcept> |
| { |
| }; |
| |
| #if defined(BOOST_ASIO_HAS_VARIABLE_TEMPLATES) |
| |
| template <typename R> |
| constexpr bool is_nothrow_start_v |
| = is_nothrow_start<R>::value; |
| |
| #endif // defined(BOOST_ASIO_HAS_VARIABLE_TEMPLATES) |
| |
| } // namespace execution |
| } // namespace asio |
| } // namespace boost |
| |
| #endif // defined(GENERATING_DOCUMENTATION) |
| |
| #include <boost/asio/detail/pop_options.hpp> |
| |
| #endif // BOOST_ASIO_EXECUTION_START_HPP |