Modifying bundled properties from visitor

Question

How should I modify the bundled properties of a vertex from inside a visitor?

I would like to use the simple method of sub-scripting the graph, but the graph parameter passed into the visitor is const, so compiler disallows changes.

I can store a reference to the graph in the visitor, but this seems weird.

/**

  A visitor which identifies vertices as leafs or trees

*/
class bfs_vis_leaf_finder:public default_bfs_visitor {

public:
    /**

    Constructor

    @param[in] total reference to int variable to store total number of leaves
    @param[in] g reference to graph ( used to modify bundled properties )

    */
    bfs_vis_leaf_finder( int& total, graph_t& g ) :
      myTotal( total ), myGraph( g )
      {
          myTotal = 0;
      }

    /**

    Called when the search finds a new vertex

    If the vertex has no children, it is a leaf and the total leaf count is incremented

    */
    template <typename Vertex, typename Graph>
    void discover_vertex( Vertex u, Graph& g)
    {
        if( out_edges( u, g ).first == out_edges( u, g ).second ) {
            myTotal++;
            //g[u].myLevel = s3d::cV::leaf;
            myGraph[u].myLevel = s3d::cV::leaf;
        } else {
            //g[u].myLevel = s3d::cV::tree;
            myGraph[u].myLevel = s3d::cV::tree;
        }
    }

    int& myTotal;
    graph_t& myGraph;
};

Answer 1

Your solution is right.

To decouple the graph type from the visitor you could pass only the interesting property map to the visitor constructor and access its elements using boost::get(property, u) = s3d::cV::leaf;. This way you can pass any type-compatible vertex property to the visitor (the visitor will be more general and not sensible to name changes in the graph type).

The type for the property map will be a template type-name for the visitor class and will be something like:

typedef property_map<graph_t, s3d_cv3_leaf_t your_vertex_info::*>::type your_property_map;

See here for a complete dissertation about bundled properties.

HTH