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  27 <a name="boost_optional.type_requirements"></a><a class="link" href="type_requirements.html" title="Type requirements">Type requirements</a>
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  29 <p>
  30       At the very minimum for <code class="computeroutput"><span class="identifier">optional</span><span class="special">&lt;</span><span class="identifier">T</span><span class="special">&gt;</span></code>
  31       to work with a minimum interface it is required that <code class="computeroutput"><span class="identifier">T</span></code>
  32       has a publicly accessible no-throw destructor. In that case you need to initialize
  33       the optional object with function <code class="computeroutput"><span class="identifier">emplace</span><span class="special">()</span></code> or use <span class="bold"><strong>InPlaceFactories</strong></span>.
  34       Additionally, if <code class="computeroutput"><span class="identifier">T</span></code> is <code class="computeroutput"><span class="identifier">Moveable</span></code>, <code class="computeroutput"><span class="identifier">optional</span><span class="special">&lt;</span><span class="identifier">T</span><span class="special">&gt;</span></code>
  35       is also <code class="computeroutput"><span class="identifier">Moveable</span></code> and can be
  36       easily initialized from an rvalue of type <code class="computeroutput"><span class="identifier">T</span></code>
  37       and be passed by value. Additionally, if <code class="computeroutput"><span class="identifier">T</span></code>
  38       is <code class="computeroutput"><span class="identifier">Copyable</span></code>, <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
  39       also <code class="computeroutput"><span class="identifier">Copyable</span></code> and can be easily
  40       initialized from an lvalue of type <code class="computeroutput"><span class="identifier">T</span></code>.
  41     </p>
  42 <p>
  43       <code class="computeroutput"><span class="identifier">T</span></code> <span class="underline">is
  44       not</span> required to be <a href="http://www.sgi.com/tech/stl/DefaultConstructible.html" target="_top">Default
  45       Constructible</a>.
  46     </p>
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