On 09.02.2010, at 02:14, Stuart Sierra wrote: > On Feb 8, 6:13 pm, aria42 <ari...@gmail.com> wrote: >> (defprotocol Span >> (start [self]) >> (stop [self]) >> (span-length [self])) >> >> Now I know I can just make span-length a function on Span as opposed >> to part of the protocol. Is that what one should do? > > Yes.
I would say "it depends". I have a similar situation in my multiarray package (http://code.google.com/p/clj-multiarray/). In the multiarray protocol, I have two functions, "shape" and "rank", with the latter being by definition the same as (comp count shape). However, I still have "rank" in the protocol, because for some implementations it is more efficient to compute the rank directly, rather than construct a shape vector just for computing its length afterwards. In such situations it is useful to provide a default implementation and leave it up to each type to implement a more efficient alternative or not. With extend and the maps that go with it, this is easy to achieve: make a map with the default implementations, and merge this with the type-specific implementations fed to extend. 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 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
