Comparison of function dispatch methods performance in Clojure

dispatch.clj

(require '[criterium.core :as c])

(defprotocol W (w [this x y]))

(def w1 (reify W (w [t x y] (* x y))))

(c/quick-bench (w w1 4 4))

; protocol dispatch
; Execution time mean : 6.625560 ns

(defrecord Wr [w])

(def w2 (Wr. (fn [x y] (* x y))))

(c/quick-bench ((:w w2) 4 4))

; function-in-record dispatch
; Execution time mean : 7.944109 ns

(def w3 {:w (fn [x y] (* x y))})

(c/quick-bench ((:w w3) 4 4))

; function-in-map dispatch
; Execution time mean : 32.106786 ns

(defmulti Wm (fn [kind x y] kind))

(defmethod Wm :w [_ x y] (* x y))

(c/quick-bench (Wm :w 4 4))

; multimethod dispatch
; Execution time mean : 44.309771 ns

; protocols are fastest, records around the same, functions in maps and multimethods slowest
; trade off is performance vs flexibility as protocols and functions-in-records can only dispatch
; on type or keyword, whereas functions-in-maps and multimethods can dispatch on vectors or anything