这是什么意思?
namespace detail { // For partial specialization workaround enum event_visitor_enum { on_no_event_num, on_initialize_vertex_num, on_start_vertex_num, on_discover_vertex_num, on_finish_vertex_num, on_examine_vertex_num, on_examine_edge_num, on_tree_edge_num, on_non_tree_edge_num, on_gray_target_num, on_black_target_num, on_forward_or_cross_edge_num, on_back_edge_num, on_edge_relaxed_num, on_edge_not_relaxed_num, on_edge_minimized_num, on_edge_not_minimized_num }; template<typename Event, typename Visitor> struct functor_to_visitor : Visitor { typedef Event event_filter; functor_to_visitor(const Visitor& visitor) : Visitor(visitor) {} }; } // namespace detail