Ken Wesson <kwess...@gmail.com> writes: > On Tue, Nov 30, 2010 at 5:27 PM, Robert McIntyre <r...@mit.edu> wrote: >> (defn runonce >> "Create a function that will only run once. All other invocations >> return the first calculated value. The function can have side effects. >> Returns a [has-run-predicate, reset-fn, once-fn]" >> [function] >> (let [sentinel (Object.) >> result (atom sentinel) >> reset-fn (fn [] (reset! result sentinel) nil) >> has-run? #(not= @result sentinel)] >> [has-run? >> reset-fn >> (fn [& args] >> (locking sentinel >> (if (= @result sentinel) >> (reset! result (function)) >> @result)))])) > > Eww. Why (locking ...)? Why not just (swap! result #(if (= % sentinel) > (function) %))?
>From the doc string: "The function can have side effects." Sometimes a lock is the right tool for the job. -- 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
