On Tue, Jul 26, 2011 at 4:00 AM, Sam Aaron <samaa...@gmail.com> wrote:
> However, it seems remarkably kludgy to encode the old value into the contract
> of the atom and *all* update fns when really this could be achieved in a much
> cleaner fashion with a version of swap! that returned a vec of new and old
> vals:
>
> (defn update-and-check-whether-modified?
> [update-fn]
> (let [[new old] (swap-and-also-return-old! (fn [v] (update-fn v)))]
> (= new old)))
This seems to have been left out:
(defn swap-and-also-return-old! [^clojure.lang.Atom a f]
(loop []
(let [v @a
nv (f v)]
(if (compare-and-set! a v nv)
[nv v]
(recur)))))
:)
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