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| <h2><span class="refentrytitle">Class template optional_last_value</span></h2> |
| <p>boost::signals2::optional_last_value — Evaluate an <a class="link" href="../../InputIterator.html" title="Concept InputIterator">InputIterator</a> 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> |
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| <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#id1157297-bb">invocation</a></span> |
| <span class="keyword">template</span><span class="special"><</span><span class="keyword">typename</span> <a class="link" href="../../InputIterator.html" title="Concept InputIterator">InputIterator</a><span class="special">></span> |
| <span class="identifier">result_type</span> <a class="link" href="optional_last_value.html#id446496-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="id2549282"></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="id2549326"></a><h3> |
| <a name="id1157297-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> <a class="link" href="../../InputIterator.html" title="Concept InputIterator">InputIterator</a><span class="special">></span> |
| <span class="identifier">result_type</span> <a name="id446496-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"> |
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| <tr> |
| <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="id2549480"></a><h3>Specializations</h3> |
| <div class="itemizedlist"><ul class="itemizedlist" type="disc"><li class="listitem"><p><a class="link" href="optional_last_value_voi_id716702.html" title="Class optional_last_value<void>">Class optional_last_value<void></a></p></li></ul></div> |
| </div> |
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| <td align="left"></td> |
| <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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