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<h2><span class="refentrytitle">Class template optional_last_value</span></h2>
<p>boost::signals2::optional_last_value — Evaluate an InputIterator sequence and return
a boost::optional which contains the last value in the sequence, or an
empty boost::optional if the sequence was empty.</p>
</div>
<h2 xmlns:rev="http://www.cs.rpi.edu/~gregod/boost/tools/doc/revision" class="refsynopsisdiv-title">Synopsis</h2>
<div xmlns:rev="http://www.cs.rpi.edu/~gregod/boost/tools/doc/revision" class="refsynopsisdiv"><pre class="synopsis"><span class="comment">// In header: <<a class="link" href="../../signals2/reference.html#header.boost.signals2.optional_last_value_hpp" title="Header <boost/signals2/optional_last_value.hpp>">boost/signals2/optional_last_value.hpp</a>>
</span><span class="keyword">template</span><span class="special"><</span><span class="keyword">typename</span> T<span class="special">></span>
<span class="keyword">class</span> <a class="link" href="optional_last_value.html" title="Class template optional_last_value">optional_last_value</a> <span class="special">{</span>
<span class="keyword">public</span><span class="special">:</span>
<span class="comment">// types</span>
<span class="keyword">typedef</span> boost::optional<span class="special"><</span><span class="identifier">T</span><span class="special">></span> <a name="boost.signals2.optional_last_value.result_type"></a><span class="identifier">result_type</span><span class="special">;</span>
<span class="comment">// <a class="link" href="optional_last_value.html#idm45507043614944-bb">invocation</a></span>
<span class="keyword">template</span><span class="special"><</span><span class="keyword">typename</span> InputIterator<span class="special">></span>
<span class="identifier">result_type</span> <a class="link" href="optional_last_value.html#idm45507043614384-bb"><span class="keyword">operator</span><span class="special">(</span><span class="special">)</span></a><span class="special">(</span><span class="identifier">InputIterator</span><span class="special">,</span> <span class="identifier">InputIterator</span><span class="special">)</span> <span class="keyword">const</span><span class="special">;</span>
<span class="special">}</span><span class="special">;</span></pre></div>
<div class="refsect1">
<a name="idm45555131357152"></a><h2>Description</h2>
<p>
<code class="computeroutput">optional_last_value</code> is the default Combiner template type for signals in the
Boost.Signals2 library. The advantage of <code class="computeroutput">optional_last_value</code> over
<a class="link" href="last_value.html" title="Class template last_value">signals2::last_value</a> is that <code class="computeroutput">optional_last_value</code>
can return an empty boost::optional. rather
than throwing an exception, when
its <code class="computeroutput">InputIterator</code> sequence is empty.
</p>
<div class="refsect2">
<a name="idm45555131352272"></a><h3>
<a name="idm45507043614944-bb"></a><code class="computeroutput">optional_last_value</code> invocation</h3>
<div class="orderedlist"><ol class="orderedlist" type="1"><li class="listitem">
<pre class="literallayout"><span class="keyword">template</span><span class="special"><</span><span class="keyword">typename</span> InputIterator<span class="special">></span>
<span class="identifier">result_type</span> <a name="idm45507043614384-bb"></a><span class="keyword">operator</span><span class="special">(</span><span class="special">)</span><span class="special">(</span><span class="identifier">InputIterator</span> first<span class="special">,</span> <span class="identifier">InputIterator</span> last<span class="special">)</span> <span class="keyword">const</span><span class="special">;</span></pre>
<div class="variablelist"><table border="0" class="variablelist compact">
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<td><p><span class="term">Effects:</span></p></td>
<td><p>Attempts to dereference every iterator in the sequence <code class="computeroutput">[first, last)</code>.
</p></td>
</tr>
<tr>
<td><p><span class="term">Returns:</span></p></td>
<td><p>
The result of the last successful iterator dereference, wrapped in a boost::optional.
The returned <code class="computeroutput">optional</code> will be empty if no iterators were dereferenced.
</p></td>
</tr>
<tr>
<td><p><span class="term">Throws:</span></p></td>
<td><p>Does not throw.</p></td>
</tr>
</tbody>
</table></div>
</li></ol></div>
</div>
<div class="refsect2">
<a name="idm45555131334672"></a><h3>Specializations</h3>
<div class="itemizedlist"><ul class="itemizedlist" style="list-style-type: disc; "><li class="listitem"><p><a class="link" href="optional_idm45507099693904.html" title="Class optional_last_value<void>">Class optional_last_value<void></a></p></li></ul></div>
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<td align="right"><div class="copyright-footer">Copyright © 2001-2004 Douglas Gregor<br>Copyright © 2007-2009 Frank Mori Hess<p>Distributed under the Boost
Software License, Version 1.0. (See accompanying file
<code class="filename">LICENSE_1_0.txt</code> or copy at <a href="http://www.boost.org/LICENSE_1_0.txt" target="_top">http://www.boost.org/LICENSE_1_0.txt</a>)</p>
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