On Fri, Dec 30, 2011 at 4:13 PM, Alan Malloy <a...@malloys.org> wrote: > On Dec 30, 11:34 am, "Marshall T. Vandegrift" <llas...@gmail.com> > wrote: >> Peter Taoussanis <ptaoussa...@gmail.com> writes: >> > Thanks- that explains it: dropping to extend works as expected. >> >> Another option I've been making use of for exactly this situation is to >> use the #= reader macro to evaluate the Class/forName at read-time. >> Something like: >> >> (extend-protocol MyProtocol >> java.lang.Integer (action [x] "Integer") >> #=(Class/forName "[B") (action [x] "ByteArray")) >> >> It may not be ideal stylistically, but lets you use extend-protocol in >> such situations. > > Stuff like this always worries me. It may happen to work now, but I > doubt if that's a guarantee. extend-protocol's contract is that you > give it a Symbol, which it resolves into a Class. It surely isn't > expecting a Class as an argument, because you can't enter that as a > source-code literal. If you give it a Class, it could conceivably do > something dreadful like try to call (resolve s) on it to figure out > what Class you mean, and that will fail when passed a Class. > > For that matter, trying out your example, it doesn't seem to work for > me. The first fix is to use java.lang.Class instead of just Class, > since reader evaluation happens in a no-frills environment. But after > that, it seems the extend-protocol just silently does nothing: > > repl-1=> (defprotocol P) > P > repl-1=> (extend-protocol P #=(java.lang.Class/forName "[B")) > nil > repl-1=> (satisfies? P (Class/forName "[B")) > false >
satisfies? works on an instance: user=> (satisfies? P (byte-array [])) true Dave -- 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
