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<title>Movable I/O Objects</title>
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<div class="titlepage"><div><div><h4 class="title">
<a name="asio.overview.cpp2011.move_objects"></a><a class="link" href="move_objects.html" title="Movable I/O Objects">Movable I/O Objects</a>
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<p>
When move support is available (via rvalue references), Asio allows move
construction and assignment of sockets, serial ports, POSIX descriptors
and Windows handles.
</p>
<p>
Move support allows you to write code like:
</p>
<pre class="programlisting"><span class="identifier">tcp</span><span class="special">::</span><span class="identifier">socket</span> <span class="identifier">make_socket</span><span class="special">(</span><span class="identifier">io_context</span><span class="special">&amp;</span> <span class="identifier">i</span><span class="special">)</span>
<span class="special">{</span>
<span class="identifier">tcp</span><span class="special">::</span><span class="identifier">socket</span> <span class="identifier">s</span><span class="special">(</span><span class="identifier">i</span><span class="special">);</span>
<span class="special">...</span>
<span class="identifier">std</span><span class="special">::</span><span class="identifier">move</span><span class="special">(</span><span class="identifier">s</span><span class="special">);</span>
<span class="special">}</span>
</pre>
<p>
or:
</p>
<pre class="programlisting"><span class="keyword">class</span> <span class="identifier">connection</span> <span class="special">:</span> <span class="keyword">public</span> <span class="identifier">enable_shared_from_this</span><span class="special">&lt;</span><span class="identifier">connection</span><span class="special">&gt;</span>
<span class="special">{</span>
<span class="keyword">private</span><span class="special">:</span>
<span class="identifier">tcp</span><span class="special">::</span><span class="identifier">socket</span> <span class="identifier">socket_</span><span class="special">;</span>
<span class="special">...</span>
<span class="keyword">public</span><span class="special">:</span>
<span class="identifier">connection</span><span class="special">(</span><span class="identifier">tcp</span><span class="special">::</span><span class="identifier">socket</span><span class="special">&amp;&amp;</span> <span class="identifier">s</span><span class="special">)</span> <span class="special">:</span> <span class="identifier">socket_</span><span class="special">(</span><span class="identifier">std</span><span class="special">::</span><span class="identifier">move</span><span class="special">(</span><span class="identifier">s</span><span class="special">))</span> <span class="special">{}</span>
<span class="special">...</span>
<span class="special">};</span>
<span class="special">...</span>
<span class="keyword">class</span> <span class="identifier">server</span>
<span class="special">{</span>
<span class="keyword">private</span><span class="special">:</span>
<span class="identifier">tcp</span><span class="special">::</span><span class="identifier">acceptor</span> <span class="identifier">acceptor_</span><span class="special">;</span>
<span class="special">...</span>
<span class="keyword">void</span> <span class="identifier">handle_accept</span><span class="special">(</span><span class="identifier">error_code</span> <span class="identifier">ec</span><span class="special">,</span> <span class="identifier">tcp</span><span class="special">::</span><span class="identifier">socket</span> <span class="identifier">socket</span><span class="special">)</span>
<span class="special">{</span>
<span class="keyword">if</span> <span class="special">(!</span><span class="identifier">ec</span><span class="special">)</span>
<span class="identifier">std</span><span class="special">::</span><span class="identifier">make_shared</span><span class="special">&lt;</span><span class="identifier">connection</span><span class="special">&gt;(</span><span class="identifier">std</span><span class="special">::</span><span class="identifier">move</span><span class="special">(</span><span class="identifier">socket</span><span class="special">))-&gt;</span><span class="identifier">go</span><span class="special">();</span>
<span class="identifier">acceptor_</span><span class="special">.</span><span class="identifier">async_accept</span><span class="special">(...);</span>
<span class="special">}</span>
<span class="special">...</span>
<span class="special">};</span>
</pre>
<p>
as well as:
</p>
<pre class="programlisting"><span class="identifier">std</span><span class="special">::</span><span class="identifier">vector</span><span class="special">&lt;</span><span class="identifier">tcp</span><span class="special">::</span><span class="identifier">socket</span><span class="special">&gt;</span> <span class="identifier">sockets</span><span class="special">;</span>
<span class="identifier">sockets</span><span class="special">.</span><span class="identifier">push_back</span><span class="special">(</span><span class="identifier">tcp</span><span class="special">::</span><span class="identifier">socket</span><span class="special">(...));</span>
</pre>
<p>
A word of warning: There is nothing stopping you from moving these objects
while there are pending asynchronous operations, but it is unlikely to
be a good idea to do so. In particular, composed operations like <a class="link" href="../../reference/async_read.html" title="async_read">async_read()</a> store a reference
to the stream object. Moving during the composed operation means that the
composed operation may attempt to access a moved-from object.
</p>
<p>
Move support is automatically enabled for <code class="literal">g++</code> 4.5 and
later, when the <code class="literal">-std=c++0x</code> or <code class="literal">-std=gnu++0x</code>
compiler options are used. It may be disabled by defining <code class="computeroutput"><span class="identifier">ASIO_DISABLE_MOVE</span></code>, or explicitly enabled
for other compilers by defining <code class="computeroutput"><span class="identifier">ASIO_HAS_MOVE</span></code>.
Note that these macros also affect the availability of <a class="link" href="move_handlers.html" title="Movable Handlers">movable
handlers</a>.
</p>
</div>
<div class="copyright-footer">Copyright © 2003-2023 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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