BGL type relation question

From: Jeff Holle (jeff.holle_at_[hidden])
Date: 2003-03-14 01:00:58

What is the relationship between an "edge_descriptor" and what an 
edge_iterator dereferences?

I'm having problems coding the following:

myFunct(GraphT& g)
{
typedef graph_traits<GraphT>::edge_descriptor Edge;
typedef map< Edge, Edge_Datum> Edge_Data;
Edge_Data edge_data;
graph_traits<GraphT>::edge_iterator ei, ei_end;
for(tie(ei,ei_end)=edges(graph);ei!=ei_end;++ei)
edge_data.insert( make_pair(*ei, Edge_Data())); << blows up here.
}