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xahaud/include/beast/core/async_completion.hpp
Vinnie Falco 8b60ef9db4 Squashed 'src/beast/' changes from 06f74f0..9f10b11
9f10b11 Set version to 1.0.0-b28
195f974 Fix HTTP split parse edge case:
264fd41 Restyle async result constructions
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git-subtree-dir: src/beast
git-subtree-split: 9f10b11eff58aeb793b673c8a8cb6e2bee3db621
2017-02-24 12:42:36 -05:00

88 lines
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C++

//
// Copyright (c) 2013-2017 Vinnie Falco (vinnie dot falco at gmail 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 BEAST_ASYNC_COMPLETION_HPP
#define BEAST_ASYNC_COMPLETION_HPP
#include <beast/core/handler_concepts.hpp>
#include <boost/asio/async_result.hpp>
#include <boost/asio/handler_type.hpp>
#include <type_traits>
#include <utility>
namespace beast {
/** Helper for customizing the return type of asynchronous initiation functions.
This class template is used to transform caller-provided completion
handlers in calls to asynchronous initiation functions. The transformation
allows customization of the return type of the initiating function, and the
function signature of the final handler.
@tparam CompletionHandler A completion handler, or a user defined type
with specializations for customizing the return type (for example,
`boost::asio::use_future` or `boost::asio::yield_context`).
@tparam Signature The callable signature of the final completion handler.
Example:
@code
...
template<class CompletionHandler>
typename async_completion<CompletionHandler,
void(error_code)>::result_type
async_initfn(..., CompletionHandler&& handler)
{
async_completion<CompletionHandler,
void(error_code)> completion{handler};
...
return completion.result.get();
}
@endcode
@note See <a href="http://www.open-std.org/jtc1/sc22/wg21/docs/papers/2014/n3896.pdf">
Library Foundations For Asynchronous Operations</a>
*/
template<class CompletionHandler, class Signature>
struct async_completion
{
/** The type of the final handler called by the asynchronous initiation function.
Objects of this type will be callable with the specified signature.
*/
using handler_type =
typename boost::asio::handler_type<
CompletionHandler, Signature>::type;
/// The type of the value returned by the asynchronous initiation function.
using result_type = typename
boost::asio::async_result<handler_type>::type;
/** Construct the helper.
@param token The completion handler. Copies will be made as
required. If `CompletionHandler` is movable, it may also be moved.
*/
async_completion(typename std::remove_reference<CompletionHandler>::type& token)
: handler(std::forward<CompletionHandler>(token))
, result(handler)
{
static_assert(is_CompletionHandler<handler_type, Signature>::value,
"Handler requirements not met");
}
/// The final completion handler, callable with the specified signature.
handler_type handler;
/// The return value of the asynchronous initiation function.
boost::asio::async_result<handler_type> result;
};
} // beast
#endif