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| <div class="titlepage"><div><div><h2 class="title" style="clear: both"> |
| <a name="move.move_and_containers"></a><a class="link" href="move_and_containers.html" title="Containers and move semantics">Containers and move semantics</a> |
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| <p> |
| Movable but non-copyable types can be safely inserted into containers and movable |
| and copyable types are more efficiently handled if those containers internally |
| use move semantics instead of copy semantics. If the container needs to "change |
| the location" of an element internally (e.g. vector reallocation) it will |
| move the element instead of copying it. <span class="bold"><strong>Boost.Container</strong></span> |
| containers are move-aware so you can write the following: |
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| <pre class="programlisting"><span class="preprocessor">#include</span> <span class="special"><</span><span class="identifier">boost</span><span class="special">/</span><span class="identifier">container</span><span class="special">/</span><span class="identifier">vector</span><span class="special">.</span><span class="identifier">hpp</span><span class="special">></span> |
| <span class="preprocessor">#include</span> <span class="special"><</span><span class="identifier">cassert</span><span class="special">></span> |
| |
| <span class="comment">//Remember: 'file_descriptor' is NOT copyable, but it</span> |
| <span class="comment">//can be returned from functions thanks to move semantics</span> |
| <span class="identifier">file_descriptor</span> <span class="identifier">create_file_descriptor</span><span class="special">(</span><span class="keyword">const</span> <span class="keyword">char</span> <span class="special">*</span><span class="identifier">filename</span><span class="special">)</span> |
| <span class="special">{</span> <span class="keyword">return</span> <span class="identifier">file_descriptor</span><span class="special">(</span><span class="identifier">filename</span><span class="special">);</span> <span class="special">}</span> |
| |
| <span class="keyword">int</span> <span class="identifier">main</span><span class="special">()</span> |
| <span class="special">{</span> |
| <span class="comment">//Open a file obtaining its descriptor, the temporary</span> |
| <span class="comment">//returned from 'create_file_descriptor' is moved to 'fd'.</span> |
| <span class="identifier">file_descriptor</span> <span class="identifier">fd</span> <span class="special">=</span> <span class="identifier">create_file_descriptor</span><span class="special">(</span><span class="string">"filename"</span><span class="special">);</span> |
| <span class="identifier">assert</span><span class="special">(!</span><span class="identifier">fd</span><span class="special">.</span><span class="identifier">empty</span><span class="special">());</span> |
| |
| <span class="comment">//Now move fd into a vector</span> |
| <span class="identifier">boost</span><span class="special">::</span><span class="identifier">container</span><span class="special">::</span><span class="identifier">vector</span><span class="special"><</span><span class="identifier">file_descriptor</span><span class="special">></span> <span class="identifier">v</span><span class="special">;</span> |
| <span class="identifier">v</span><span class="special">.</span><span class="identifier">push_back</span><span class="special">(</span><span class="identifier">boost</span><span class="special">::</span><span class="identifier">move</span><span class="special">(</span><span class="identifier">fd</span><span class="special">));</span> |
| |
| <span class="comment">//Check ownership has been transferred</span> |
| <span class="identifier">assert</span><span class="special">(</span><span class="identifier">fd</span><span class="special">.</span><span class="identifier">empty</span><span class="special">());</span> |
| <span class="identifier">assert</span><span class="special">(!</span><span class="identifier">v</span><span class="special">[</span><span class="number">0</span><span class="special">].</span><span class="identifier">empty</span><span class="special">());</span> |
| |
| <span class="comment">//Compilation error if uncommented since file_descriptor is not copyable</span> |
| <span class="comment">//and vector copy construction requires value_type's copy constructor:</span> |
| <span class="comment">//boost::container::vector<file_descriptor> v2(v);</span> |
| <span class="keyword">return</span> <span class="number">0</span><span class="special">;</span> |
| <span class="special">}</span> |
| </pre> |
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| <td align="right"><div class="copyright-footer">Copyright © 2008-2014 Ion Gaztanaga<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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