78 lines
6.3 KiB
HTML
78 lines
6.3 KiB
HTML
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<html>
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<head>
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<meta http-equiv="Content-Type" content="text/html; charset=UTF-8">
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<title>Movable Handlers</title>
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<link rel="stylesheet" href="../../../boostbook.css" type="text/css">
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<meta name="generator" content="DocBook XSL Stylesheets V1.75.2">
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<link rel="home" href="../../../index.html" title="Asio">
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<link rel="up" href="../cpp2011.html" title="C++ 2011 Support">
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<link rel="prev" href="move_objects.html" title="Movable I/O Objects">
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<link rel="next" href="variadic.html" title="Variadic Templates">
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<meta name="viewport" content="width=device-width, initial-scale=1">
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</head>
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<body bgcolor="white" text="black" link="#0000FF" vlink="#840084" alink="#0000FF">
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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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<hr>
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<div class="spirit-nav">
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<a accesskey="p" href="move_objects.html"><img src="../../../prev.png" alt="Prev"></a><a accesskey="u" href="../cpp2011.html"><img src="../../../up.png" alt="Up"></a><a accesskey="h" href="../../../index.html"><img src="../../../home.png" alt="Home"></a><a accesskey="n" href="variadic.html"><img src="../../../next.png" alt="Next"></a>
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</div>
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<div class="section">
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<div class="titlepage"><div><div><h4 class="title">
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<a name="asio.overview.cpp2011.move_handlers"></a><a class="link" href="move_handlers.html" title="Movable Handlers">Movable Handlers</a>
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</h4></div></div></div>
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<p>
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With C++11 and later, user-defined completion handlers are only required
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to be move constructible, and are not required to be copy constructible.
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</p>
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<p>
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When move support is enabled, asynchronous that are documented as follows:
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</p>
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<pre class="programlisting"><span class="keyword">template</span> <span class="special"><</span><span class="keyword">typename</span> <span class="identifier">Handler</span><span class="special">></span>
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<span class="keyword">void</span> <span class="identifier">async_XYZ</span><span class="special">(...,</span> <span class="identifier">Handler</span> <span class="identifier">handler</span><span class="special">);</span>
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</pre>
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<p>
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are actually declared as:
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</p>
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<pre class="programlisting"><span class="keyword">template</span> <span class="special"><</span><span class="keyword">typename</span> <span class="identifier">Handler</span><span class="special">></span>
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<span class="keyword">void</span> <span class="identifier">async_XYZ</span><span class="special">(...,</span> <span class="identifier">Handler</span><span class="special">&&</span> <span class="identifier">handler</span><span class="special">);</span>
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</pre>
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<p>
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The handler argument is perfectly forwarded and the move construction occurs
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within the body of <code class="computeroutput"><span class="identifier">async_XYZ</span><span class="special">()</span></code>. This ensures that all other function
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arguments are evaluated prior to the move. This is critical when the other
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arguments to <code class="computeroutput"><span class="identifier">async_XYZ</span><span class="special">()</span></code> are members of the handler. For example:
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</p>
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<pre class="programlisting"><span class="keyword">struct</span> <span class="identifier">my_operation</span>
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<span class="special">{</span>
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<span class="identifier">unique_ptr</span><span class="special"><</span><span class="identifier">tcp</span><span class="special">::</span><span class="identifier">socket</span><span class="special">></span> <span class="identifier">socket</span><span class="special">;</span>
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<span class="identifier">unique_ptr</span><span class="special"><</span><span class="identifier">vector</span><span class="special"><</span><span class="keyword">char</span><span class="special">>></span> <span class="identifier">buffer</span><span class="special">;</span>
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<span class="special">...</span>
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<span class="keyword">void</span> <span class="keyword">operator</span><span class="special">(</span><span class="identifier">error_code</span> <span class="identifier">ec</span><span class="special">,</span> <span class="identifier">size_t</span> <span class="identifier">length</span><span class="special">)</span>
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<span class="special">{</span>
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<span class="special">...</span>
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<span class="identifier">socket</span><span class="special">-></span><span class="identifier">async_read_some</span><span class="special">(</span><span class="identifier">asio</span><span class="special">::</span><span class="identifier">buffer</span><span class="special">(*</span><span class="identifier">buffer</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="keyword">this</span><span class="special">));</span>
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<span class="special">...</span>
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<span class="special">}</span>
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<span class="special">};</span>
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</pre>
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<p>
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Move support is automatically enabled for <code class="literal">g++</code> 4.5 and
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later, when the <code class="literal">-std=c++0x</code> or <code class="literal">-std=gnu++0x</code>
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compiler options are used. It may be disabled by defining <code class="computeroutput"><span class="identifier">ASIO_DISABLE_MOVE</span></code>, or explicitly enabled
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for other compilers by defining <code class="computeroutput"><span class="identifier">ASIO_HAS_MOVE</span></code>.
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Note that these macros also affect the availability of <a class="link" href="move_objects.html" title="Movable I/O Objects">movable
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I/O objects</a>.
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</p>
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</div>
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<div class="copyright-footer">Copyright © 2003-2023 Christopher 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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</div>
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<hr>
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<div class="spirit-nav">
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<a accesskey="p" href="move_objects.html"><img src="../../../prev.png" alt="Prev"></a><a accesskey="u" href="../cpp2011.html"><img src="../../../up.png" alt="Up"></a><a accesskey="h" href="../../../index.html"><img src="../../../home.png" alt="Home"></a><a accesskey="n" href="variadic.html"><img src="../../../next.png" alt="Next"></a>
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</div>
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</body>
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</html>
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