[boost] [Graph] Improved creation of visitors from function objects

From: Douglas Gregor (gregod_at_[hidden])
Date: 2003-04-16 09:32:14

Creating new visitors in the BGL can be a pain, because it may require a lot 
of extra typing for simple cases. I'd like to add the ability to attach 
function objects to visitor events like this:

  dfs_visitor<>()
    .do_on_back_edge(var(has_cycle) = true)
    .do_on_tree_edge(bind(&vector<edge>::push_back, ref(tree_edges), _1));

I'd really prefer "on_XXX" instead of "do_on_XXX", but GCC trips over the 
former syntax. Anyway, the code is ready to check in if there are no 
objections. The patch isn't very large, but is bigger than I would like to 
post here.

        Doug