I don't understand your domain of course, but the way I'd do this would be a slight variant of OPTION 1
> >> get_forces(a::AbstractAtom) = error("All AbstractAtom subtypes should >> implement get_forces") >> get_forces(a::Atom) = get_forces(a.calc) >> >> > this is indeed what I've done at the moment. Good to hear that this is not > completely idiotic. > Ok, actually this is slightly different - so I don't understand why this would help? Many thanks, Christoph > >