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<p>
      <code class="computeroutput"><span class="identifier">optional</span><span class="special">&lt;</span><span class="identifier">T</span><span class="special">&gt;</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/move constructor and <code class="computeroutput"><span class="identifier">T</span></code>'s
      destructor are explicitly used to initialize, copy, move 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 &#169; 2003-2007 Fernando Luis Cacciola Carballal<br>Copyright &#169; 2014 Andrzej Krzemie&#324;ski<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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