Does this help?: http://fulldisclojure.blogspot.com/2010/08/thoughts-on-protocols.html
And Sean's comment here: http://programming-puzzler.blogspot.com/2010/08/racket-vs-clojure.html Regards, Shantanu On Aug 12, 5:46 pm, Laurent PETIT <laurent.pe...@gmail.com> wrote: > Hi, > > 2010/8/12 Matthew <mattp...@gmail.com> > > > > > > > > > > > Hello all, > > > I've been looking at the new protocol (defprotocol, deftype, > > defrecord, etc) feature in 1.2 and, while I love the core concepts, > > it's been bothering me that there's no apparent way to provide > > *automatic* default implementations for methods on a protocol. > > > I know from reading Rich Hickey's discussions on the design rationale > > [1] and other threads on providing Scala Trait-like behaviour [2] that > > you can choose to mix in a set of defaults when you implement the > > protocol, but it seems important to me that a protocol author be able > > to provide default implementations to enable protocols to evolve. > > Allowing a function body in the defprotocol clause would seem to be > > the obvious way, something like: > > > (defprotocol P > > (foo [x] (default-foo x)) > > (bar-me [x] (bar-me [1 x]) > > [x y])) ; no default implementation > > > As I'm sure most of you know, a key problem with "pure" interface > > features in environments like CORBA, COM, Java, etc has been that you > > can't add new methods to published interfaces: you'd break all > > existing implementations. Hence you see a history of evolving > > interfaces indicated by names like IFoo, IFoo2, IFooEx, etc. In > > contrast, a Scala-like trait system allows you to add a new method > > *and* a default implementation (supposing that makes sense), so old > > clients still work fine. > > > The problem, as I see it, with Clojure protocols is that you would > > have to rely on clients mixing in a set of defaults in order to > > happily extend a "public" protocol. > > > Am I missing something key here? I realise there are some very > > experienced people contributing to Clojure, so am fully expecting to > > be told I've missed something obvious ;) > > Maybe have the library writer do this ? : > > (defprotocol P > (foo [x] (default-foo x)) > (bar-me [x] (bar-me [1 x]) > [x y])) ; no default implementation > > (def *P-defaults* > {:foo default-foo > :bar-me #(bar-me 1 %) }) > > and let the user pick the whole *P-defaults* for its mixins, or just parts > of it ? (does this make sense ?) > > > > > > > > > > > Cheers, > > > Matthew. > > > [1]http://groups.google.com/group/clojure/msg/330c230e8dc857a9 > > [2]http://groups.google.com/group/clojure/msg/53228e04db4799a5 > > > -- > > 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<clojure%2bunsubscr...@googlegroups.com > > > > > For more options, visit this group at > >http://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
