async_compose.html
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<table cellpadding="2" width="100%"><tr><td valign="top"><img alt="asio C++ library" width="250" height="60" src="../../asio.png"></td></tr></table>
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<div class="titlepage"><div><div><h3 class="title">
<a name="asio.reference.async_compose"></a><a class="link" href="async_compose.html" title="async_compose">async_compose</a>
</h3></div></div></div>
<p>
<a class="indexterm" name="asio.indexterm.async_compose"></a>
Launch an asynchronous operation
with a stateful implementation.
</p>
<pre class="programlisting">template<
typename CompletionToken,
typename Signature,
typename Implementation,
typename... IoObjectsOrExecutors>
<a class="link" href="asynchronous_operations.html#asio.reference.asynchronous_operations.automatic_deduction_of_initiating_function_return_type"><span class="emphasis"><em>DEDUCED</em></span></a> async_compose(
Implementation && implementation,
CompletionToken & token,
IoObjectsOrExecutors &&... io_objects_or_executors);
</pre>
<p>
The async_compose function simplifies the implementation of composed asynchronous
operations automatically wrapping a stateful function object with a conforming
intermediate completion handler.
</p>
<h5>
<a name="asio.reference.async_compose.h0"></a>
<span><a name="asio.reference.async_compose.parameters"></a></span><a class="link" href="async_compose.html#asio.reference.async_compose.parameters">Parameters</a>
</h5>
<div class="variablelist">
<p class="title"><b></b></p>
<dl>
<dt><span class="term">implementation</span></dt>
<dd><p>
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.
</p></dd>
<dt><span class="term">token</span></dt>
<dd><p>
The completion token.
</p></dd>
<dt><span class="term">io_objects_or_executors</span></dt>
<dd><p>
Zero or more I/O objects or I/O executors for which outstanding work
must be maintained.
</p></dd>
</dl>
</div>
<h5>
<a name="asio.reference.async_compose.h1"></a>
<span><a name="asio.reference.async_compose.example_"></a></span><a class="link" href="async_compose.html#asio.reference.async_compose.example_">Example:</a>
</h5>
<pre class="programlisting">struct async_echo_implementation
{
tcp::socket& socket_;
asio::mutable_buffer buffer_;
enum { starting, reading, writing } state_;
template <typename Self>
void operator()(Self& self,
asio::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;
asio::async_write(socket_, buffer_,
asio::transfer_exactly(n),
std::move(self));
}
break;
case writing:
self.complete(error, n);
break;
}
}
};
template <typename CompletionToken>
auto async_echo(tcp::socket& socket,
asio::mutable_buffer buffer,
CompletionToken&& token) ->
typename asio::async_result<
typename std::decay<CompletionToken>::type,
void(asio::error_code, std::size_t)>::return_type
{
return asio::async_compose<CompletionToken,
void(asio::error_code, std::size_t)>(
async_echo_implementation{socket, buffer,
async_echo_implementation::starting},
token, socket);
}
</pre>
<h5>
<a name="asio.reference.async_compose.h2"></a>
<span><a name="asio.reference.async_compose.requirements"></a></span><a class="link" href="async_compose.html#asio.reference.async_compose.requirements">Requirements</a>
</h5>
<p>
<span class="emphasis"><em>Header: </em></span><code class="literal">asio/compose.hpp</code>
</p>
<p>
<span class="emphasis"><em>Convenience header: </em></span><code class="literal">asio.hpp</code>
</p>
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<td align="right"><div class="copyright-footer">Copyright © 2003-2020 Christopher M.
Kohlhoff<p>
Distributed under the Boost Software License, Version 1.0. (See accompanying
file LICENSE_1_0.txt or copy at <a href="http://www.boost.org/LICENSE_1_0.txt" target="_top">http://www.boost.org/LICENSE_1_0.txt</a>)
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