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//
// async_result.hpp
// ~~~~~~~~~~~~~~~~
//
// Copyright (c) 2003-2018 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 ASIO_ASYNC_RESULT_HPP
#define ASIO_ASYNC_RESULT_HPP
#if defined(_MSC_VER) && (_MSC_VER >= 1200)
# pragma once
#endif // defined(_MSC_VER) && (_MSC_VER >= 1200)
#include "asio/detail/config.hpp"
#include "asio/detail/type_traits.hpp"
#include "asio/handler_type.hpp"
#include "asio/detail/push_options.hpp"
namespace asio {
/// An interface for customising the behaviour of an initiating function.
/**
* The async_result traits class is used for determining:
*
* @li the concrete completion handler type to be called at the end of the
* asynchronous operation;
*
* @li the initiating function return type; and
*
* @li how the return value of the initiating function is obtained.
*
* The trait allows the handler and return types to be determined at the point
* where the specific completion handler signature is known.
*
* This template may be specialised for user-defined completion token types.
* The primary template assumes that the CompletionToken is the completion
* handler.
*/
#if defined(ASIO_NO_DEPRECATED) || defined(GENERATING_DOCUMENTATION)
template <typename CompletionToken, typename Signature>
#else // defined(ASIO_NO_DEPRECATED) || defined(GENERATING_DOCUMENTATION)
template <typename CompletionToken, typename Signature = void>
#endif // defined(ASIO_NO_DEPRECATED) || defined(GENERATING_DOCUMENTATION)
class async_result
{
public:
#if defined(ASIO_NO_DEPRECATED) || defined(GENERATING_DOCUMENTATION)
/// The concrete completion handler type for the specific signature.
typedef CompletionToken completion_handler_type;
/// The return type of the initiating function.
typedef void return_type;
#else // defined(ASIO_NO_DEPRECATED) || defined(GENERATING_DOCUMENTATION)
// For backward compatibility, determine the concrete completion handler type
// by using the legacy handler_type trait.
typedef typename handler_type<CompletionToken, Signature>::type
completion_handler_type;
// For backward compatibility, determine the initiating function return type
// using the legacy single-parameter version of async_result.
typedef typename async_result<completion_handler_type>::type return_type;
#endif // defined(ASIO_NO_DEPRECATED) || defined(GENERATING_DOCUMENTATION)
/// Construct an async result from a given handler.
/**
* When using a specalised async_result, the constructor has an opportunity
* to initialise some state associated with the completion handler, which is
* then returned from the initiating function.
*/
explicit async_result(completion_handler_type& h)
#if defined(ASIO_NO_DEPRECATED) || defined(GENERATING_DOCUMENTATION)
// No data members to initialise.
#else // defined(ASIO_NO_DEPRECATED) || defined(GENERATING_DOCUMENTATION)
: legacy_result_(h)
#endif // defined(ASIO_NO_DEPRECATED) || defined(GENERATING_DOCUMENTATION)
{
(void)h;
}
/// Obtain the value to be returned from the initiating function.
return_type get()
{
#if defined(ASIO_NO_DEPRECATED) || defined(GENERATING_DOCUMENTATION)
// Nothing to do.
#else // defined(ASIO_NO_DEPRECATED) || defined(GENERATING_DOCUMENTATION)
return legacy_result_.get();
#endif // defined(ASIO_NO_DEPRECATED) || defined(GENERATING_DOCUMENTATION)
}
private:
async_result(const async_result&) ASIO_DELETED;
async_result& operator=(const async_result&) ASIO_DELETED;
#if defined(ASIO_NO_DEPRECATED) || defined(GENERATING_DOCUMENTATION)
// No data members.
#else // defined(ASIO_NO_DEPRECATED) || defined(GENERATING_DOCUMENTATION)
async_result<completion_handler_type> legacy_result_;
#endif // defined(ASIO_NO_DEPRECATED) || defined(GENERATING_DOCUMENTATION)
};
#if !defined(ASIO_NO_DEPRECATED)
/// (Deprecated: Use two-parameter version of async_result.) An interface for
/// customising the behaviour of an initiating function.
/**
* This template may be specialised for user-defined handler types.
*/
template <typename Handler>
class async_result<Handler>
{
public:
/// The return type of the initiating function.
typedef void type;
/// Construct an async result from a given handler.
/**
* When using a specalised async_result, the constructor has an opportunity
* to initialise some state associated with the handler, which is then
* returned from the initiating function.
*/
explicit async_result(Handler&)
{
}
/// Obtain the value to be returned from the initiating function.
type get()
{
}
};
#endif // !defined(ASIO_NO_DEPRECATED)
/// Helper template to deduce the handler type from a CompletionToken, capture
/// a local copy of the handler, and then create an async_result for the
/// handler.
template <typename CompletionToken, typename Signature>
struct async_completion
{
/// The real handler type to be used for the asynchronous operation.
typedef typename asio::async_result<
typename decay<CompletionToken>::type,
Signature>::completion_handler_type completion_handler_type;
#if defined(ASIO_HAS_MOVE) || defined(GENERATING_DOCUMENTATION)
/// Constructor.
/**
* The constructor creates the concrete completion handler and makes the link
* between the handler and the asynchronous result.
*/
explicit async_completion(CompletionToken& token)
: completion_handler(static_cast<typename conditional<
is_same<CompletionToken, completion_handler_type>::value,
completion_handler_type&, CompletionToken&&>::type>(token)),
result(completion_handler)
{
}
#else // defined(ASIO_HAS_MOVE) || defined(GENERATING_DOCUMENTATION)
explicit async_completion(typename decay<CompletionToken>::type& token)
: completion_handler(token),
result(completion_handler)
{
}
explicit async_completion(const typename decay<CompletionToken>::type& token)
: completion_handler(token),
result(completion_handler)
{
}
#endif // defined(ASIO_HAS_MOVE) || defined(GENERATING_DOCUMENTATION)
/// A copy of, or reference to, a real handler object.
#if defined(ASIO_HAS_MOVE) || defined(GENERATING_DOCUMENTATION)
typename conditional<
is_same<CompletionToken, completion_handler_type>::value,
completion_handler_type&, completion_handler_type>::type completion_handler;
#else // defined(ASIO_HAS_MOVE) || defined(GENERATING_DOCUMENTATION)
completion_handler_type completion_handler;
#endif // defined(ASIO_HAS_MOVE) || defined(GENERATING_DOCUMENTATION)
/// The result of the asynchronous operation's initiating function.
async_result<typename decay<CompletionToken>::type, Signature> result;
};
namespace detail {
template <typename CompletionToken, typename Signature>
struct async_result_helper
: async_result<typename decay<CompletionToken>::type, Signature>
{
};
} // namespace detail
} // namespace asio
#include "asio/detail/pop_options.hpp"
#if defined(GENERATING_DOCUMENTATION)
# define ASIO_INITFN_RESULT_TYPE(ct, sig) \
void_or_deduced
#elif defined(_MSC_VER) && (_MSC_VER < 1500)
# define ASIO_INITFN_RESULT_TYPE(ct, sig) \
typename ::asio::detail::async_result_helper< \
ct, sig>::return_type
#define ASIO_HANDLER_TYPE(ct, sig) \
typename ::asio::detail::async_result_helper< \
ct, sig>::completion_handler_type
#else
# define ASIO_INITFN_RESULT_TYPE(ct, sig) \
typename ::asio::async_result< \
typename ::asio::decay<ct>::type, sig>::return_type
#define ASIO_HANDLER_TYPE(ct, sig) \
typename ::asio::async_result< \
typename ::asio::decay<ct>::type, sig>::completion_handler_type
#endif
#endif // ASIO_ASYNC_RESULT_HPP
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