In the API it is suggested to use `seq` to check if coll is empty. I was working on some code recently found that my biggest performance bottleneck was calling `seq` to check for emptiness. The calls to `seq` were causing lots of object allocation and taking noticeable CPU time. I switched to using `identical?` to explicitly compare against the empty vector and was rewarded with a drastic reduction in execution time.
Here are some hasty tests showing just how big the difference can be: user=> (let [iterations 100000000] (time (dotimes [_ iterations] (identical? [] []))) (time (dotimes [_ iterations] (seq [])))) "Elapsed time: 3.512 msecs" "Elapsed time: 2512.366 msecs" nil user=> (let [iterations 100000000] (time (dotimes [_ iterations] (identical? "" ""))) (time (dotimes [_ iterations] (seq "")))) "Elapsed time: 3.898 msecs" "Elapsed time: 5607.865 msecs" nil user=> (let [iterations 100000000] (time (dotimes [_ iterations] (identical? () ()))) (time (dotimes [_ iterations] (seq ())))) "Elapsed time: 3.768 msecs" "Elapsed time: 2258.095 msecs" nil Has any thought been given to providing a faster `empty?` that is not based on seq? Thanks, Eric Kobrin -- 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
