All simple Reader/Writer mechanisms are going to move to an encapsulated state machine model. The idea is that code is often shared between Readers and Writers that accomplish the same thing but are simply driven in different ways (the former by output, the latter by input). Classes that would be immediately affected: ios::FilterMap, ios::Base64Reader, ios::Base64Writer. Classes that would eventually be affected: api::zlib::DeflateBuffer, api::zlib::InflateBuffer.