reducers string/join

gistfile1.clj

(defn str-join
 ([] nil)
 (^String [^String x ^String y]
   (if (and x y) (.. (new StringBuilder x)
                     (append "\n")
                     (append y)
                     toString)
     (if x x
       (if y y)))))

(defn str-join-2
  [strs]
    (clojure.string/join "\n" strs))

(defn str-join-3
 ([] nil)
 ([x y]
    (if (and x y) (str x "\n" y)
        (if x (str x)
            (if y (str y))))))

(require '[clojure.core.reducers :as r])
(require '[criterium.core :refer [quick-bench bench]])

(quick-bench (r/fold str-join ["1" "2" "3" "4" "5"]))

;;             Execution time mean : 490.672257 ns
;;    Execution time std-deviation : 71.757578 ns
;;   Execution time lower quantile : 447.661789 ns ( 2.5%)
;;   Execution time upper quantile : 610.315252 ns (97.5%)
;;                   Overhead used : 112.290565 ns`

(quick-bench (r/fold str-join-3 ["1" "2" "3" "4" "5"]))

;;             Execution time mean : 1.239270 µs
;;    Execution time std-deviation : 118.953022 ns
;;   Execution time lower quantile : 1.100272 µs ( 2.5%)
;;   Execution time upper quantile : 1.365724 µs (97.5%)
;;                   Overhead used : 112.290565 ns

(quick-bench (r/fold str-join (repeat 100000 "test")))

;;             Execution time mean : 17.564645 sec
;;    Execution time std-deviation : 120.251706 ms
;;   Execution time lower quantile : 17.495060 sec ( 2.5%)
;;   Execution time upper quantile : 17.771489 sec (97.5%)
;;                   Overhead used : 112.290565 ns

(quick-bench (r/fold str-join-3 (repeat 100000 "test")))

;;             Execution time mean : 18.218646 sec
;;    Execution time std-deviation : 537.798381 ms
;;   Execution time lower quantile : 17.459723 sec ( 2.5%)
;;   Execution time upper quantile : 18.768461 sec (97.5%)
;;                   Overhead used : 112.290565 ns