Hi all,
This is mainly a question for the Clojure core dev team. I'm trying really hard to understand the thinking behind the new IAtom2 interface. My train of thought is detailed below, but you don't have to read the full thing. The core question is "How come the existing IAtom didn't grow, given the fact that you guys *own* the interface?"
OK so here is the full story:
I recently found out about
https://dev.clojure.org/jira/browse/CLJ-1454, and it's true that
often you want a version of `swap!` that returns the value that
was swapped *out*. As indicated on the ticket various people have
worked around the lack of such a fn in various ways. The solution
that I'm using/maintaining looks very much like the approach taken
with IAtom2, only it's goes through a protocol and it's written in
clojure. Basically I've defined a new abstraction and extending it
to Atom.
(defprotocol IAtomic ... ;; more methods (trade! [this f] [this f x] [this f x y] [this f x y more] "Like `clojure.core/swap!`, but returns the value that was swapped out.")) (defmacro ^:private trade* [ref f & args] `(let [validate# (.getValidator ~ref)] ;; extract the validator-fn once (loop [] (let [oldv# (.deref ~ref) newv# (~f oldv# ~@args)] (try (when-not (validate# newv#) (throw (IllegalStateException. "Invalid reference state"))) (catch Exception e# (IllegalStateException. "Invalid reference state" ) e#)) (if (.compareAndSet ~ref oldv# newv#) (do (.notifyWatches ~ref oldv# newv#) oldv#) (recur)))))) (extend-protocol IAtomic ... ;; more types Atom (trade! ([this f] (trade* this f)) ([this f x] (trade* this f x)) ([this f x y] (trade* this f x y)) ([this f x y more] (trade* this #(apply f % x y more))) ) )
Ok, so at this point I want to stress out that the way I see it this solution seems to me like the second best option. I say 'second', because IMO the best option would be to add `trade!` (or however you want to call it) to the original IAtom.java and implement it straight in Atom.java. But obviously I can't do that - only clojure.core can. Since clojure.core didn't, I'd say that it's safe to assume that either a) growing IAtom is not desirable, and/or b) having IAtom2 is a superior solution . Personally, I wouldn't be able to explain/defend any of those in a conversation. I'm probably missing something here, and that's exactly why I'm sending this email. Enlighten me please... :) what am i missing? How come IAtom was, in some sense, cloned, rather than grown? Many thanks in advance...
Jim
ps: oh and btw congrats on the 1.9 release :)
--
You received this message because you are subscribed to the Google
Groups "Clojure" group.
To post to this group, send email to clo...@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+unsubscribe@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 unsubscribe from this group and stop receiving emails from it, send an email to clojure+unsubscribe@googlegroups.com.
For more options, visit https://groups.google.com/d/optout.
Hi all,
This is mainly a question for the Clojure core dev team. I'm trying really hard to understand the thinking behind the new IAtom2 interface. My train of thought is detailed below, but you don't have to read the full thing. The core question is "How come the existing IAtom didn't grow, given the fact that you guys *own* the interface?"