On Mar 20, 2009, at 16:18, Rich Hickey wrote: >> Providing a :default implementation for multimethods is a very common >> and useful technique, but it is really useful only for multimethods >> that dispatch on a single argument. > > I disagree about that. No dispatch value, composite or not, is still a > valid concept.
True, for reasons other than a default in a type hierarchy. >> But suppose you want to provide a default for one argument only? >> Something like >> >> (defmethod + [java.lang.Integer ::any] ...) >> > > I think it is best to think about this differently than :default, it's > more about a universal parent than about a missing dispatch value. It could be seen from both points of view (universal parent in the hierarchy, or a partial match with a default), but I agree that the universal parent point of view makes more sense. >> Would it be a good idea to provide the possiblity to add a universal >> parent to hierarchies? Or would that create any problems? Is there >> another solution for the situation I described? > > Yes, don't know, and no. I briefly looked at this but only got as far > as to decide Object couldn't be the universal parent. I think you have > to reserve a value that will never otherwise be used. Object would indeed not work, the universal parent would have to be even above Object. I just looked at the implementation of hierarchies and I have the impression that this should be rather simple to implement. I will try and see how it works out in practice. Konrad. --~--~---------~--~----~------------~-------~--~----~ You received this message because you are subscribed to the Google Groups "Clojure" group. To post to this group, send email to clojure@googlegroups.com To unsubscribe from this group, send email to clojure+unsubscr...@googlegroups.com For more options, visit this group at http://groups.google.com/group/clojure?hl=en -~----------~----~----~----~------~----~------~--~---
