| <html> |
| <head> |
| <meta http-equiv="Content-Type" content="text/html; charset=ISO-8859-1"> |
| <title>Optional references</title> |
| <link rel="stylesheet" href="../boostbook.css" type="text/css"> |
| <meta name="generator" content="DocBook XSL Stylesheets V1.75.2"> |
| <link rel="home" href="../index.html" title="Chapter 1. Boost.Optional"> |
| <link rel="up" href="../index.html" title="Chapter 1. Boost.Optional"> |
| <link rel="prev" href="examples.html" title="Examples"> |
| <link rel="next" href="rebinding_semantics_for_assignment_of_optional_references.html" title="Rebinding semantics for assignment of optional references"> |
| </head> |
| <body bgcolor="white" text="black" link="#0000FF" vlink="#840084" alink="#0000FF"> |
| <table cellpadding="2" width="100%"><tr> |
| <td valign="top"><img alt="Boost C++ Libraries" width="277" height="86" src="../../../../../boost.png"></td> |
| <td align="center"><a href="../../../../../index.html">Home</a></td> |
| <td align="center"><a href="../../../../libraries.htm">Libraries</a></td> |
| <td align="center"><a href="http://www.boost.org/users/people.html">People</a></td> |
| <td align="center"><a href="http://www.boost.org/users/faq.html">FAQ</a></td> |
| <td align="center"><a href="../../../../../more/index.htm">More</a></td> |
| </tr></table> |
| <hr> |
| <div class="spirit-nav"> |
| <a accesskey="p" href="examples.html"><img src="../../../../../doc/html/images/prev.png" alt="Prev"></a><a accesskey="u" href="../index.html"><img src="../../../../../doc/html/images/up.png" alt="Up"></a><a accesskey="h" href="../index.html"><img src="../../../../../doc/html/images/home.png" alt="Home"></a><a accesskey="n" href="rebinding_semantics_for_assignment_of_optional_references.html"><img src="../../../../../doc/html/images/next.png" alt="Next"></a> |
| </div> |
| <div class="section" title="Optional references"> |
| <div class="titlepage"><div><div><h2 class="title" style="clear: both"> |
| <a name="boost_optional.optional_references"></a><a class="link" href="optional_references.html" title="Optional references">Optional references</a> |
| </h2></div></div></div> |
| <p> |
| This library allows the template parameter <code class="computeroutput"><span class="identifier">T</span></code> |
| 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> |
| <span class="keyword">const</span><span class="special">&</span></code>. |
| </p> |
| <p> |
| However, since references are not real objects some restrictions apply and |
| some operations are not available in this case: |
| </p> |
| <div class="itemizedlist"><ul class="itemizedlist" type="disc"> |
| <li class="listitem"> |
| Converting constructors |
| </li> |
| <li class="listitem"> |
| Converting assignment |
| </li> |
| <li class="listitem"> |
| InPlace construction |
| </li> |
| <li class="listitem"> |
| InPlace assignment |
| </li> |
| <li class="listitem"> |
| Value-access via pointer |
| </li> |
| </ul></div> |
| <p> |
| 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> |
| treats it wrapped pseudo-object much as a real value, a true real reference |
| is stored so aliasing will ocurr: |
| </p> |
| <div class="itemizedlist"><ul class="itemizedlist" type="disc"> |
| <li class="listitem"> |
| Copies of <code class="computeroutput"><span class="identifier">optional</span><span class="special"><</span><span class="identifier">T</span><span class="special">&></span></code> |
| will copy the references but all these references will nonetheless reefer |
| to the same object. |
| </li> |
| <li class="listitem"> |
| Value-access will actually provide access to the referenced object rather |
| than the reference itself. |
| </li> |
| </ul></div> |
| </div> |
| <table xmlns:rev="http://www.cs.rpi.edu/~gregod/boost/tools/doc/revision" width="100%"><tr> |
| <td align="left"></td> |
| <td align="right"><div class="copyright-footer">Copyright © 2003 -2007 Fernando Luis Cacciola Carballal<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>) |
| </p> |
| </div></td> |
| </tr></table> |
| <hr> |
| <div class="spirit-nav"> |
| <a accesskey="p" href="examples.html"><img src="../../../../../doc/html/images/prev.png" alt="Prev"></a><a accesskey="u" href="../index.html"><img src="../../../../../doc/html/images/up.png" alt="Up"></a><a accesskey="h" href="../index.html"><img src="../../../../../doc/html/images/home.png" alt="Home"></a><a accesskey="n" href="rebinding_semantics_for_assignment_of_optional_references.html"><img src="../../../../../doc/html/images/next.png" alt="Next"></a> |
| </div> |
| </body> |
| </html> |