https://gcc.gnu.org/bugzilla/show_bug.cgi?id=113099
--- Comment #8 from Jonathan Wakely <redi at gcc dot gnu.org> --- (In reply to Peter Dimov from comment #7) > You don't necessarily need dynamic_cast because facets are always installed > and obtained by their exact type, not via a reference to base. Is that true? std::use_facet<X> will return a reference to a facet with X::id but it could actually be something derived from X. e.g. a user can install their own facet derived from std::ctype<char>, which overrides some members. Code that does std::use_facet<std::ctype<char>>(loc) will get the user's facet, but via reference to base. > You can store > the Facet* as given (like shared_ptr does), and return it. > > The only reason dynamic_cast is needed here is because you can't static_cast > from facet* to Facet* when virtual inheritance. But you are not required to > store facet* in the actual container; you can store the original Facet* as > void*. An implementation could do that, but I don't think libstdc++ can do it now without an ABI change.
