Re: [Boost-users] [BGL] filtered graph missing vertex function

From: moritz Hilger (moritz.hilger_at_[hidden])
Date: 2006-09-05 18:58:39

On 9/5/06, Stephan Diederich <S.Diederich_at_[hidden]> wrote:
>
> Hi Moritz,
>
> 2006/9/5, moritz Hilger <moritz.hilger_at_[hidden]>:
> - Zitierten Text anzeigen -
> > is there a particular reason that the filtered graph is missing a
> > vertex_descriptor vertex(vertices_size_type, const& filtered_graph)
> > function? of course this would return exactly the same as the one of the
> > underlying graph, nevertheless it would be handy for code treating
> filtered
> > graphs the same way as normal ones.
>
> I think the problem here is the return value of the function. If you
> have a VertexPredicate set, it would be possible that the vertex you
> specify through the index doesn't exist in the filtered graph.
> Maybe a null_vertex() could be returned in that case (But, IIRC, that
> null_vertex() doesn't exist in every graph).

hmm, the null_vertex() function is part of the graph concept (
http://www.boost.org/libs/graph/doc/Graph.html) and  should return "a
special boost::graph_traits<G>::vertex_descriptor object which does not
refer to any vertex of graph object which type is G." so why not return this
if the VertexPredicate excludes the requested vertex?
cheers,
moritz