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//
// compose.hpp
// ~~~~~~~~~~~
//
// Copyright (c) 2003-2025 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_COMPOSE_HPP
#define BOOST_ASIO_COMPOSE_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/composed.hpp>
#include <boost/asio/detail/push_options.hpp>
namespace boost {
namespace asio {
/// Launch an asynchronous operation with a stateful implementation.
/**
* The async_compose function simplifies the implementation of composed
* asynchronous operations automatically wrapping a stateful function object
* with a conforming intermediate completion handler.
*
* @param implementation A function object that contains the implementation of
* the composed asynchronous operation. The first argument to the function
* object is a non-const reference to the enclosing intermediate completion
* handler. The remaining arguments are any arguments that originate from the
* completion handlers of any asynchronous operations performed by the
* implementation.
*
* @param token The completion token.
*
* @param io_objects_or_executors Zero or more I/O objects or I/O executors for
* which outstanding work must be maintained.
*
* @par Per-Operation Cancellation
* By default, terminal per-operation cancellation is enabled for
* composed operations that are implemented using @c async_compose. To
* disable cancellation for the composed operation, or to alter its
* supported cancellation types, call the @c self object's @c
* reset_cancellation_state function.
*
* @par Example:
*
* @code struct async_echo_implementation
* {
* tcp::socket& socket_;
* boost::asio::mutable_buffer buffer_;
* enum { starting, reading, writing } state_;
*
* template <typename Self>
* void operator()(Self& self,
* boost::system::error_code error = {},
* std::size_t n = 0)
* {
* switch (state_)
* {
* case starting:
* state_ = reading;
* socket_.async_read_some(
* buffer_, std::move(self));
* break;
* case reading:
* if (error)
* {
* self.complete(error, 0);
* }
* else
* {
* state_ = writing;
* boost::asio::async_write(socket_, buffer_,
* boost::asio::transfer_exactly(n),
* std::move(self));
* }
* break;
* case writing:
* self.complete(error, n);
* break;
* }
* }
* };
*
* template <typename CompletionToken>
* auto async_echo(tcp::socket& socket,
* boost::asio::mutable_buffer buffer,
* CompletionToken&& token)
* -> decltype(
* boost::asio::async_compose<CompletionToken,
* void(boost::system::error_code, std::size_t)>(
* std::declval<async_echo_implementation>(),
* token, socket))
* {
* return boost::asio::async_compose<CompletionToken,
* void(boost::system::error_code, std::size_t)>(
* async_echo_implementation{socket, buffer,
* async_echo_implementation::starting},
* token, socket);
* } @endcode
*/
template <typename CompletionToken, typename Signature,
typename Implementation, typename... IoObjectsOrExecutors>
inline auto async_compose(Implementation&& implementation,
type_identity_t<CompletionToken>& token,
IoObjectsOrExecutors&&... io_objects_or_executors)
-> decltype(
async_initiate<CompletionToken, Signature>(
composed<Signature>(static_cast<Implementation&&>(implementation),
static_cast<IoObjectsOrExecutors&&>(io_objects_or_executors)...),
token))
{
return async_initiate<CompletionToken, Signature>(
composed<Signature>(static_cast<Implementation&&>(implementation),
static_cast<IoObjectsOrExecutors&&>(io_objects_or_executors)...),
token);
}
} // namespace asio
} // namespace boost
#include <boost/asio/detail/pop_options.hpp>
#endif // BOOST_ASIO_COMPOSE_HPP