You could create a local instance of clojure.lang.MultiFn in a let binding, and access it directly. You can see the definition of the object here:
http://github.com/richhickey/clojure/blob/master/src/jvm/clojure/lang/MultiFn.java The very good reason you DO NOT DO THIS is that this object is MUTABLE. I STRONGLY RECOMMEND that you use a dispatch fn that returns a keyword, and use that to select a closure from a hash map for local bindings. Sean On May 17, 10:41 am, Mikhail Kryshen <mikh...@kryshen.net> wrote: > 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. > > 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? > > -- > Mikhail > > -- > 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 > athttp://groups.google.com/group/clojure?hl=en -- 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
