Hi, I would like to know if it is safe to create a struct and make it inherit from a multi_index. Actually I already tried but I got this error: /usr/include/boost/multi_index_container.hpp:204: warning: base class 'struct boost::multi_index::detail::header_holder<boost::multi_index::detail::ordered_index_node<boost::multi_index::detail::index_node_base<vcsn::InitialValue<vcsn::rat::exp<std::basic_string<char, std::char_traits<char>, std::allocator<char> >, float> > > >, boost::multi_index::multi_index_container< [...] >, boost::multi_index::indexed_by<boost::multi_index::ordered_unique<boost::multi_index::member<vcsn::InitialValue<vcsn::rat::exp<std::basic_string<char, std::char_traits<char>, std::allocator<char> >, float> >, [...] >' should be explicitly initialized in the copy constructor Is it an issue due to Boost or because I'm doing something really bad? Thanks, -- Guillaume Lazzara Epita CSI 2008