re class="literal-block">
// new overload
BOOST_PARAMETER_FUNCTION(
    (void), depth_first_search, (tag), (required (graph,*))( … ))
{
    // new algorithm implementation
}

…

// ambiguous!
depth_first_search(boost::adjacency_list&lt;&gt;(), 2, &quot;hello&quot;);
</pre>
<!-- @ignore() -->
<div class="section" id="adding-type-requirements">
<h5>2.1.5.6.1&nbsp;&nbsp;&nbsp;Adding Type Requirements</h5>
<p>We really don't want the compiler to consider the original version
of <tt class="docutils literal">