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<title>Implementation Notes</title>
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<div class="titlepage"><div><div><h2 class="title" style="clear: both">
<a name="boost_optional.implementation_notes"></a><a class="link" href="implementation_notes.html" title="Implementation Notes">Implementation Notes</a>
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<p>
<code class="computeroutput"><span class="identifier">optional</span><span class="special"><</span><span class="identifier">T</span><span class="special">></span></code> is
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>
(both from Type Traits). It uses a separate boolean flag to indicate the initialization
state. Placement new with <code class="computeroutput"><span class="identifier">T</span></code>'s
copy constructor and <code class="computeroutput"><span class="identifier">T</span></code>'s destructor
are explicitly used to initialize,copy and destroy optional values. As a result,
<code class="computeroutput"><span class="identifier">T</span></code>'s default constructor is
effectively by-passed, but the exception guarantees are basic. It is planned
to replace the current implementation with another with stronger 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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<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>)
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