Hi all, I want to use a map to cache values based on a key. I'm planning to use an atom for this. My basic operation is "give me the value for this key" - if the value exists in the map then that value should be returned, otherwise a new value should be calculated, inserted in the map and then returned. My plan is to implement something like the following:
(defn ensure [cache key] (if (contains? cache key) cache (assoc cache key (calc-value key))))(let [value (get (swap! cache ensure key) key)] ... do my thing with value ...) So 'ensure' ensures that the cache contains the value for key, the swap! operation returns the cache with the value and then I get it out. This works but feels a little clumsy, is there a better way to do this? Also, looking at the Atom source code, I see that this will cause a CAS operation even if the value returned from swap! is identical to the original value. It seems like a reasonable optimisation would be to check if the values are identical and not update if so - is there a reason this might not be a good idea? Thanks, Colin -- 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 --- 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+unsubscr...@googlegroups.com. For more options, visit https://groups.google.com/d/optout.
