Hi, Trying to compile our ALPS project sources (http://alps.comp- phys.org) with the CVS HEAD I encountered a number of problems with the BGL concept checking. In particular on MacOS X, using the Apple g+ + 4.0.1, I encounter problems in depth_first_search.hpp with: template <class Visitor, class Graph> class DFSVisitorConcept { public: void constraints() { function_requires< CopyConstructibleConcept<Visitor> >(); vis.initialize_vertex(u, g); vis.start_vertex(u, g); vis.discover_vertex(u, g); vis.examine_edge(e, g); vis.tree_edge(e, g); vis.back_edge(e, g); vis.forward_or_cross_edge(e, g); vis.finish_vertex(u, g); } private: Visitor vis; Graph g; typename graph_traits<Graph>::vertex_descriptor u; typename graph_traits<Graph>::edge_descriptor e; }; Somehow this tries to instantiate a default constructor for the visitor and the graph. Since some graph types do not have a default constructor and no default constructor should actually be required, I want to ask whether this is a bug in the compiler or in the concept checks? Matthias