title: BGL: map objects to graphs
body: <p>I need to be able to store a graph type Tree for every vertex in a given graph. I am trying to use <code>boost::ptr_map&lt;vertex_desc, Tree&gt; DESC</code> where <code>Tree</code> is a adjacency list graph type. After i create a Tree object <code>desc</code> and add the vertices I want, I try to store desc to the map like that <code>DESC.insert(std::make_pair(*vi.first, desc))</code> but the compiler doesn't allow it. If I 
  do <code>DESC[*vi.first] = desc</code> the compiler doesn't complain but after that I encounter very strange behavior when i try to use the map. Should I use another way of storing the Tree object?  </p>