[Boost-users] [BGL] implementing operator < for edge_descriptors

Hello, I am trying to create a std::map. Unfortunaltely, there is no less operator defined for edge descriptors, so i'd like to implement my own version based on a custom internal property associated with the edge. Is it possible to access an arbitrary property, solely based on an edge_descriptor without having access to the graph object? Here some pseudo-code: struct compare_edge_descriptors { bool operator()(edge_descriptor e1, edge_descriptor e2) { unsigned int val1 = get_property_somehow(e1.get_property(), my_custom_property); unsigned int val2 = get_property_somehow(e2.get_property(), my_custom_property); return (val1 < val2 ); } }; Do you have an idea how to implement "get_property_somehow"? Thanks, Max