support C++11, see <a href="http://www.boost.org/doc/libs/release/libs/type_traits/doc/html/boost_typetraits/reference/is_copy_constructible.html" target="_top"><code class="computeroutput">boost::is_copy_constructible</code></a>):</p>
<pre class="programlisting"><span class="keyword">class</span> <span class="identifier">u</span><span class="special">;</span> <span class="comment">// Some user-defined type for which old values shall not be copied.</span>

<span class="keyword">namespace</span> <span class=