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<title>Optional references</title>
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<link rel="start" href="../index.html" title="Chapter<65>1.<2E>Boost.Optional">
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semantics for assignment of optional references">
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<div class="section" lang="en">
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<div class="titlepage"><div><div><h2 class="title" style="clear: both">
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<a name="boost_optional.optional_references"></a><a href="optional_references.html" title="Optional references">Optional references</a>
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</h2></div></div></div>
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<p>
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This library allows the template parameter <code class="computeroutput"><span class="identifier">T</span></code>
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to be of reference type: <code class="computeroutput"><span class="identifier">T</span><span class="special">&</span></code>, and to some extent, <code class="computeroutput"><span class="identifier">T</span>
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<span class="keyword">const</span><span class="special">&</span></code>.
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</p>
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<p>
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However, since references are not real objects some restrictions apply and
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some operations are not available in this case:
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</p>
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<div class="itemizedlist"><ul type="disc">
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<li>
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Converting constructors
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</li>
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<li>
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Converting assignment
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</li>
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<li>
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InPlace construction
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</li>
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<li>
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InPlace assignment
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</li>
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<li>
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Value-access via pointer
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</li>
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</ul></div>
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<p>
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Also, even though <code class="computeroutput"><span class="identifier">optional</span><span class="special"><</span><span class="identifier">T</span><span class="special">&></span></code>
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treats it wrapped pseudo-object much as a real value, a true real reference
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is stored so aliasing will ocurr:
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</p>
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<div class="itemizedlist"><ul type="disc">
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<li>
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Copies of <code class="computeroutput"><span class="identifier">optional</span><span class="special"><</span><span class="identifier">T</span><span class="special">&></span></code>
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will copy the references but all these references will nonetheless reefer
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to the same object.
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</li>
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<li>
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Value-access will actually provide access to the referenced object rather
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than the reference itself.
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</li>
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</ul></div>
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</div>
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<table xmlns:rev="http://www.cs.rpi.edu/~gregod/boost/tools/doc/revision" width="100%"><tr>
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<td align="left"></td>
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<td align="right"><small>Copyright <20> 2003 -2007 Fernando Luis Cacciola Carballal</small></td>
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</tr></table>
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<hr>
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