2010/5/17 Mikhail Kryshen <mikh...@kryshen.net>: > On 17 май, 12:07, Laurent PETIT <laurent.pe...@gmail.com> wrote: >> Yes, >> >> as David wrote, >> >> What you're describing is not single-dispatch-based polymorphism (e.g. >> like in java), it's double dispatch (because you want to dispatch to >> the implementation of the protocol function based on both the type and >> another parameter which may be totally dynamic, or materialized -when >> serialized- by some key in the configuration - spring bean name, >> etc.). > > That makes sense. It looks like I was trying to avoid explicit > double-dispatch by manipulating the protocol at runtime. Is it abuse > of dynamic features of Clojure? > >> Protocols are based on a single dispatch mechanism, as classical >> "class based" languages (e.g. Java) are. >> >> When you write "kind of expandability almost free with well-designed >> OO systems", I guess this design implies some kind of implementation >> of the Strategy pattern, or more probably Delegation pattern. > > What I was actually talking about is the possibility to avoid global > state and being able to extend existing implementation to multiple > instances without much refactoring.
Not sure it's of interest for your particular case, but note that as far as protocols are concerned, you can have a per-instance protocol implementation (à la java anonymous classes) by using reify. > Protocols and multimethods both have global state. From what I saw in > Clojure source protocols are manipulated by changing root binding of > associated var, and multimethods are actually mutable functions > changed by defmethod (I see inconsistency here). > > There is no standard way to create multimethod or protocol without > binding it to global var. Why is it possible to create non-global > function but not multimethod? I'll let people with more knowledge than me answer those ones :-) -- 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 Note that posts from new members are moderated - please be patient with your first post. 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
