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<div class="titlepage"><div><div><h2 class="title" style="clear: both">
<a name="move.move_iterator"></a><a class="link" href="move_iterator.html" title="Move iterators">Move iterators</a>
</h2></div></div></div>
<pre class="programlisting"><span class="keyword">template</span><span class="special"><</span><span class="keyword">class</span> <span class="identifier">Iterator</span><span class="special">></span>
<span class="keyword">class</span> <span class="identifier">move_iterator</span><span class="special">;</span>
<span class="keyword">template</span><span class="special"><</span><span class="keyword">class</span> <span class="identifier">It</span><span class="special">></span>
<span class="identifier">move_iterator</span><span class="special"><</span><span class="identifier">It</span><span class="special">></span> <span class="identifier">make_move_iterator</span><span class="special">(</span><span class="keyword">const</span> <span class="identifier">It</span> <span class="special">&</span><span class="identifier">it</span><span class="special">);</span>
</pre>
<p>
<code class="computeroutput"><a class="link" href="../boost/move_iterator.html" title="Class template move_iterator">move_iterator</a></code> is an iterator
adaptor with the same behavior as the underlying iterator except that its dereference
operator implicitly converts the value returned by the underlying iterator's
dereference operator to a rvalue reference: <code class="computeroutput"><span class="identifier">boost</span><span class="special">::</span><span class="identifier">move</span><span class="special">(*</span><span class="identifier">underlying_iterator</span><span class="special">)</span></code>
It is a read-once iterator, but can have up to random access traversal characteristics.
</p>
<p>
<code class="computeroutput"><span class="identifier">move_iterator</span></code> is very useful
because some generic algorithms and container insertion functions can be called
with move iterators to replace copying with moving. For example:
</p>
<p>
</p>
<pre class="programlisting"><span class="comment">//header file "movable.hpp"</span>
<span class="preprocessor">#include</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">core</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">boost</span><span class="special">/</span><span class="identifier">move</span><span class="special">/</span><span class="identifier">traits</span><span class="special">.</span><span class="identifier">hpp</span><span class="special">></span>
<span class="comment">//A movable class</span>
<span class="keyword">class</span> <span class="identifier">movable</span>
<span class="special">{</span>
<span class="identifier">BOOST_MOVABLE_BUT_NOT_COPYABLE</span><span class="special">(</span><span class="identifier">movable</span><span class="special">)</span>
<span class="keyword">int</span> <span class="identifier">value_</span><span class="special">;</span>
<span class="keyword">public</span><span class="special">:</span>
<span class="identifier">movable</span><span class="special">()</span> <span class="special">:</span> <span class="identifier">value_</span><span class="special">(</span><span class="number">1</span><span class="special">){}</span>
<span class="comment">//Move constructor and assignment</span>
<span class="identifier">movable</span><span class="special">(</span><span class="identifier">BOOST_RV_REF</span><span class="special">(</span><span class="identifier">movable</span><span class="special">)</span> <span class="identifier">m</span><span class="special">)</span>
<span class="special">{</span> <span class="identifier">value_</span> <span class="special">=</span> <span class="identifier">m</span><span class="special">.</span><span class="identifier">value_</span><span class="special">;</span> <span class="identifier">m</span><span class="special">.</span><span class="identifier">value_</span> <span class="special">=</span> <span class="number">0</span><span class="special">;</span> <span class="special">}</span>
<span class="identifier">movable</span> <span class="special">&</span> <span class="keyword">operator</span><span class="special">=(</span><span class="identifier">BOOST_RV_REF</span><span class="special">(</span><span class="identifier">movable</span><span class="special">)</span> <span class="identifier">m</span><span class="special">)</span>
<span class="special">{</span> <span class="identifier">value_</span> <span class="special">=</span> <span class="identifier">m</span><span class="special">.</span><span class="identifier">value_</span><span class="special">;</span> <span class="identifier">m</span><span class="special">.</span><span class="identifier">value_</span> <span class="special">=</span> <span class="number">0</span><span class="special">;</span> <span class="keyword">return</span> <span class="special">*</span><span class="keyword">this</span><span class="special">;</span> <span class="special">}</span>
<span class="keyword">bool</span> <span class="identifier">moved</span><span class="special">()</span> <span class="keyword">const</span> <span class="comment">//Observer</span>
<span class="special">{</span> <span class="keyword">return</span> <span class="special">!</span><span class="identifier">value_</span><span class="special">;</span> <span class="special">}</span>
<span class="keyword">int</span> <span class="identifier">value</span><span class="special">()</span> <span class="keyword">const</span> <span class="comment">//Observer</span>
<span class="special">{</span> <span class="keyword">return</span> <span class="identifier">value_</span><span class="special">;</span> <span class="special">}</span>
<span class="special">};</span>
<span class="keyword">namespace</span> <span class="identifier">boost</span><span class="special">{</span>
<span class="keyword">template</span><span class="special"><></span>
<span class="keyword">struct</span> <span class="identifier">has_nothrow_move</span><span class="special"><</span><span class="identifier">movable</span><span class="special">></span>
<span class="special">{</span>
<span class="keyword">static</span> <span class="keyword">const</span> <span class="keyword">bool</span> <span class="identifier">value</span> <span class="special">=</span> <span class="keyword">true</span><span class="special">;</span>
<span class="special">};</span>
<span class="special">}</span> <span class="comment">//namespace boost{</span>
</pre>
<p>
</p>
<p>
<code class="computeroutput"><span class="identifier">movable</span></code> objects can be moved
from one container to another using move iterators and insertion and assignment
operations.w
</p>
<p>
</p>
<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="string">"movable.hpp"</span>
<span class="preprocessor">#include</span> <span class="special"><</span><span class="identifier">cassert</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="keyword">using</span> <span class="keyword">namespace</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="comment">//Create a vector with 10 default constructed objects</span>
<span class="identifier">vector</span><span class="special"><</span><span class="identifier">movable</span><span class="special">></span> <span class="identifier">v</span><span class="special">(</span><span class="number">10</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">moved</span><span class="special">());</span>
<span class="comment">//Move construct all elements in v into v2</span>
<span class="identifier">vector</span><span class="special"><</span><span class="identifier">movable</span><span class="special">></span> <span class="identifier">v2</span><span class="special">(</span> <span class="identifier">boost</span><span class="special">::</span><span class="identifier">make_move_iterator</span><span class="special">(</span><span class="identifier">v</span><span class="special">.</span><span class="identifier">begin</span><span class="special">())</span>
<span class="special">,</span> <span class="identifier">boost</span><span class="special">::</span><span class="identifier">make_move_iterator</span><span class="special">(</span><span class="identifier">v</span><span class="special">.</span><span class="identifier">end</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">moved</span><span class="special">());</span>
<span class="identifier">assert</span><span class="special">(!</span><span class="identifier">v2</span><span class="special">[</span><span class="number">0</span><span class="special">].</span><span class="identifier">moved</span><span class="special">());</span>
<span class="comment">//Now move assign all elements from in v2 back into v</span>
<span class="identifier">v</span><span class="special">.</span><span class="identifier">assign</span><span class="special">(</span> <span class="identifier">boost</span><span class="special">::</span><span class="identifier">make_move_iterator</span><span class="special">(</span><span class="identifier">v2</span><span class="special">.</span><span class="identifier">begin</span><span class="special">())</span>
<span class="special">,</span> <span class="identifier">boost</span><span class="special">::</span><span class="identifier">make_move_iterator</span><span class="special">(</span><span class="identifier">v2</span><span class="special">.</span><span class="identifier">end</span><span class="special">()));</span>
<span class="identifier">assert</span><span class="special">(</span><span class="identifier">v2</span><span class="special">[</span><span class="number">0</span><span class="special">].</span><span class="identifier">moved</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">moved</span><span class="special">());</span>
<span class="keyword">return</span> <span class="number">0</span><span class="special">;</span>
<span class="special">}</span>
</pre>
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