/span><span class="special">&gt;</span> <span class="special">:</span> <span class="identifier">boost</span><span class="special">::</span><span class="identifier">false_type</span> <span class="special">{</span><span class="special">}</span><span class="special">;</span>
<span class="special">}</span> <span class="special">}</span> <span class="comment">// namespace</span>
</pre>
<p>A given old value type <code class="computeroutput">T</code> is copied only if <code class="computeroutput">boost::contract::