[boost] Boost Graph Library: Dijkstra Shortest Path ignores color_map in named parameters?

1 Jul 2010

      I am trying to use the dijkstra_shortest_path algorithm with named 
parameters. It worked well, until I wanted to pass the color map as an 
argument.

Despite providing my own color_map, the algorithm ends up creating its 
own two_bit_color_map.

I am using the following code:

template<class TGraph, class TVisitor>
int myDijkstra(TGraph& graph, TVisitor& visitor, int source)
{
        bool earlyExit = false;

        const int nVertices =boost::num_vertices(graph);

        std::vector<double> distances(nVertices);
        std::vector<typename TGraph::vertex_descriptor> 
predecessors(nVertices);
        std::vector<boost::default_color_type> colors(nVertices);

        try {
            boost::dijkstra_shortest_paths<TSubGraph, TVisitor >(
                graph, source,
                boost::predecessor_map( &predecessors[0]  )
                .distance_map( &distances[0]  )
                .visitor( visitor )
                .color_map( &colors[0] )
            );
        } catch( EarlyExitByVisitor ) {
            earlyExit = true;
        }
        return earlyExit ? CountBlackVertices(colors) : nVertices;
}

The code compiles and runs, but the vector of colors is never modified 
(I can initialize it with different colors, makes no difference).
The predecessor and distance maps are  fine.

Tracing what happens in the source code (boost version 1.43). I notice 
that the Named Parameter Variant (line 466)  gets the distance, weight 
and index from the named parameter object. It then passes on to the 
dijkstra_dispatch1 (line 443) that adds the default for the distance 
map. It passes on to dijkstra_dispatch2 (line 413) that sets even more 
parameters, but not the color map. Finally it calls 
dijkstra_shortest_paths variant with default color_map (line 342), which 
ignores the named parameter object and provides its own color map. (all 
of the line numbers are in file dijkstra_shortest_paths.hpp).

My question is: is this a bug? Can I use named parameters if I want to 
provide my own color_map? How?

Any help is appreciated.

-- 
Alex Hagen-Zanker