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26 | <div class="titlepage"><div><div><h2 class="title" style="clear: both"> | |
27 | <a name="boost_optional.implementation_notes"></a><a class="link" href="implementation_notes.html" title="Implementation Notes">Implementation Notes</a> | |
28 | </h2></div></div></div> | |
29 | <p> | |
30 | <code class="computeroutput"><span class="identifier">optional</span><span class="special"><</span><span class="identifier">T</span><span class="special">></span></code> is | |
31 | currently implemented using a custom aligned storage facility built from <code class="computeroutput"><span class="identifier">alignment_of</span></code> and <code class="computeroutput"><span class="identifier">type_with_alignment</span></code> | |
32 | (both from Type Traits). It uses a separate boolean flag to indicate the initialization | |
33 | state. Placement new with <code class="computeroutput"><span class="identifier">T</span></code>'s | |
34 | copy/move constructor and <code class="computeroutput"><span class="identifier">T</span></code>'s | |
35 | destructor are explicitly used to initialize, copy, move and destroy optional | |
36 | values. As a result, <code class="computeroutput"><span class="identifier">T</span></code>'s default | |
37 | constructor is effectively by-passed, but the exception guarantees are basic. | |
38 | It is planned to replace the current implementation with another with stronger | |
39 | exception safety, such as a future <code class="computeroutput"><span class="identifier">boost</span><span class="special">::</span><span class="identifier">variant</span></code>. | |
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42 | <table xmlns:rev="http://www.cs.rpi.edu/~gregod/boost/tools/doc/revision" width="100%"><tr> | |
43 | <td align="left"></td> | |
44 | <td align="right"><div class="copyright-footer">Copyright © 2003-2007 Fernando Luis Cacciola Carballal<br>Copyright © 2014 Andrzej Krzemieński<p> | |
45 | Distributed under the Boost Software License, Version 1.0. (See accompanying | |
46 | 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>) | |
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