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158 lines
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<title>async_compose</title>
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<div class="titlepage"><div><div><h3 class="title">
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<a name="boost_asio.reference.async_compose"></a><a class="link" href="async_compose.html" title="async_compose">async_compose</a>
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</h3></div></div></div>
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<p>
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<a class="indexterm" name="boost_asio.indexterm.async_compose"></a>
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Launch an asynchronous operation
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with a stateful implementation.
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</p>
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<pre class="programlisting">template<
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typename CompletionToken,
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typename Signature,
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typename Implementation,
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typename... IoObjectsOrExecutors>
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<a class="link" href="asynchronous_operations.html#boost_asio.reference.asynchronous_operations.automatic_deduction_of_initiating_function_return_type"><span class="emphasis"><em>DEDUCED</em></span></a> async_compose(
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Implementation && implementation,
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CompletionToken & token,
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IoObjectsOrExecutors &&... io_objects_or_executors);
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</pre>
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<p>
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The async_compose function simplifies the implementation of composed asynchronous
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operations automatically wrapping a stateful function object with a conforming
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intermediate completion handler.
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</p>
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<h5>
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<a name="boost_asio.reference.async_compose.h0"></a>
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<span class="phrase"><a name="boost_asio.reference.async_compose.parameters"></a></span><a class="link" href="async_compose.html#boost_asio.reference.async_compose.parameters">Parameters</a>
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</h5>
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<div class="variablelist">
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<p class="title"><b></b></p>
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<dl class="variablelist">
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<dt><span class="term">implementation</span></dt>
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<dd><p>
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A function object that contains the implementation of the composed
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asynchronous operation. The first argument to the function object is
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a non-const reference to the enclosing intermediate completion handler.
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The remaining arguments are any arguments that originate from the completion
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handlers of any asynchronous operations performed by the implementation.
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</p></dd>
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<dt><span class="term">token</span></dt>
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<dd><p>
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The completion token.
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</p></dd>
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<dt><span class="term">io_objects_or_executors</span></dt>
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<dd><p>
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Zero or more I/O objects or I/O executors for which outstanding work
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must be maintained.
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</p></dd>
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</dl>
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</div>
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<h5>
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<a name="boost_asio.reference.async_compose.h1"></a>
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<span class="phrase"><a name="boost_asio.reference.async_compose.example_"></a></span><a class="link" href="async_compose.html#boost_asio.reference.async_compose.example_">Example:</a>
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</h5>
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<pre class="programlisting">struct async_echo_implementation
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{
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tcp::socket& socket_;
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boost::asio::mutable_buffer buffer_;
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enum { starting, reading, writing } state_;
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template <typename Self>
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void operator()(Self& self,
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boost::system::error_code error = {},
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std::size_t n = 0)
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{
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switch (state_)
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{
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case starting:
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state_ = reading;
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socket_.async_read_some(
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buffer_, std::move(self));
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break;
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case reading:
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if (error)
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{
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self.complete(error, 0);
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}
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else
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{
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state_ = writing;
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boost::asio::async_write(socket_, buffer_,
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boost::asio::transfer_exactly(n),
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std::move(self));
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}
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break;
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case writing:
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self.complete(error, n);
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break;
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}
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}
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};
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template <typename CompletionToken>
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auto async_echo(tcp::socket& socket,
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boost::asio::mutable_buffer buffer,
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CompletionToken&& token) ->
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typename boost::asio::async_result<
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typename std::decay<CompletionToken>::type,
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void(boost::system::error_code, std::size_t)>::return_type
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{
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return boost::asio::async_compose<CompletionToken,
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void(boost::system::error_code, std::size_t)>(
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async_echo_implementation{socket, buffer,
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async_echo_implementation::starting},
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token, socket);
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}
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</pre>
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<h5>
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<a name="boost_asio.reference.async_compose.h2"></a>
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<span class="phrase"><a name="boost_asio.reference.async_compose.requirements"></a></span><a class="link" href="async_compose.html#boost_asio.reference.async_compose.requirements">Requirements</a>
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</h5>
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<p>
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<span class="emphasis"><em>Header: </em></span><code class="literal">boost/asio/compose.hpp</code>
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</p>
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<p>
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<span class="emphasis"><em>Convenience header: </em></span><code class="literal">boost/asio.hpp</code>
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</p>
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</div>
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<table xmlns:rev="http://www.cs.rpi.edu/~gregod/boost/tools/doc/revision" width="100%"><tr>
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<td align="left"></td>
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<td align="right"><div class="copyright-footer">Copyright © 2003-2021 Christopher
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M. Kohlhoff<p>
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Distributed under the Boost Software License, Version 1.0. (See accompanying
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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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</p>
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