</tt>.<br>
  <b>Default:</b> <tt>D()</tt>with
   <tt>D=typename property_traits&lt;DistanceMap&gt;::value_type</tt><br>
</blockquote>
  
OUT: <tt>visitor(DijkstraVisitor v)</tt>  
<blockquote>
  Use this to specify actions that you would like to happen
  during certain event points within the algorithm.
  The type <tt>DijkstraVisitor</tt> must be a model of the
  <a href="./DijkstraVisitor.html">Dijkstra Visitor</a> concept. 
 The visitor object is passed by value <a
  href="#2">[2]</a>.<br>
  <b>Default:</