[Boost-users] [BGL] vis passed by value to depth_first_visit

Subject: [Boost-users] [BGL] vis passed by value to depth_first_visit
From: Shaun Jackman (sjackman_at_[hidden])
Date: 2011-04-19 20:06:54

Hi, 

I recently learned the hard way that the visitor parameter, vis, is
passed by value to depth_first_visit, but passed by reference to
detail::depth_first_visit_impl.

I was writing a function that implemented depth_first_search, but starts
each of the visits at vertices with indegree == 0. If my
depth_first_search replacement calls boost::depth_first_visit, each call
to depth_first_visit makes a copy of the output iterator, which doesn't
work for an output iterator with any state (such as a pointer).

Calling an internal boost function like detail::depth_first_visit_impl
doesn't seem like a good plan. How should I solve this?

My short-term work around is to use an output iterator that does not
have any state, such as a back_inserter.

Cheers,
Shaun