As some may know, I am working on a Unicode library that I plan to submit to Boost fairly soon. The codecs in that library are based around iterators and ranges, but since there was some demand for support for codecvt facets I am working on adapting those into that form as well. Unfortunately, it seems it is only possible to subclass std::codecvt<char, char, mbstate_t> and std::codecvt<wchar_t, char, mbstate_t>. I personally don't know and understand that much about iostreams/locales, but I have looked quickly at libstdc++'s implementation and it doesn't seem like it is possible for std::locale to contain any other instance of codecvt. What I wonder is if there is really a point to facets, then. std::codecvt<wchar_t, char, mbstate_t> means that the in-memory charset would be UTF-16 or UTF-32 (depending on the size of wchar_t) while the file would be UTF-8. The problem is that wchar_t is platform-dependent and not really reliable, so it's not really something I'd recommend to use as the in-memory representation to deal with Unicode. Why do people even use utf8_codecvt_facet anyway? What's wrong with dealing with UTF-8 rather than maybe UTF-16 or UTF-32?