Hi all, Can someone explain me why I get an error with the first one and not the second? 1) (error) boost::dijkstra_shortest_paths(m_ugraph,*vertex_iterator_begin, boost::distance_map(boost::make_iterator_property_map(dist_map.begin(), boost::get(boost::vertex_index, m_ugraph))), boost::visitor(dijkstra_vis( *vertex_iterator_begin, superStorage ) )); 2) (good) boost::dijkstra_shortest_paths(m_ugraph,*vertex_iterator_begin, boost::distance_map(boost:: make_iterator_property_map(dist_map.begin(), boost::get(boost::vertex_index, m_ugraph))).visitor(dijkstra_vis( *vertex_iterator_begin, superStorage )) ); Why I need to "." the visitor on the distance_map? BFS is ok with it: (good) boost::breadth_first_search(m_ugraph, *vertex_iterator_begin , boost ::visitor(bfs_vis( *vertex_iterator_begin, superStorage ) )); Best, Tasos