[boost] [Filesystem] Hidden overloaded virtual function

./boost/detail/utf8_codecvt_facet.hpp:171:17: warning: 'boost::filesystem::detail::utf8_codecvt_facet::do_length' hides overloaded virtual function [-Woverloaded-virtual] virtual int do_length( ^ /usr/include/c++/v1/__locale:952:17: note: hidden overloaded virtual function 'std::__1::codecvt<wchar_t, char, __mbstate_t>::do_length' declared here: type mismatch at 1st parameter ('state_type &' (aka '__mbstate_t &') vs 'const std::mbstate_t &' (aka 'const __mbstate_t &')) virtual int do_length(state_type&, const extern_type* __frm, const extern_type* __end, size_t __mx) const; ^ I suspect that's not intentional. Ben