[boost] [BGL] Why source() needs a graph argument?

Subject: [boost] [BGL] Why source() needs a graph argument?
From: Cosimo Calabrese (cosimo.calabrese_at_[hidden])
Date: 2009-10-02 07:12:23

Hi to all,

the question is in subject. I don't understand it. Either source() and 
target() functions only return the m_source member and the m_target of 
edge_base. They don't use the graph argument, that is not even used.

I need to know it because I'm implementing an union_graph adaptor, that 
provides the join's view of 2 graph. When I call the source() function 
on a union_graph, I provide an edge_descriptor; but whereas the source() 
function of an adjacency_list needs a graph argument, I need to know 
which graph belongs the edge, which is an 2 * O|E| operation on 2 graphs.

Thanks,
Cosimo Calabrese