Both of FAST decoders (OnixS::FIX::FAST::Decoder and OnixS::FIX::FAST::EventBasedDecoder) could be initialized in dictionary-independent mode. This means that there is no need to specify FIX Dictionary for a Decoder's constructor. The decoder will generate appropriate dictionary basing on the FAST template content. Generated Dictionary will be accessible via OnixS::FIX::FAST::Decoder::fixDictionary and becomes permanent for the Engine (until OnixS::FIX::Engine::shutdown called).
It is quite similar to using of the OnixS::FIX::FAST::Decoder::generateFixDictionary method, but the dictionary identifier is chosen by the decoder itself on the base of FAST template content.