assoc 3-arity vs var-args arity performance comparison, see: https://twitter.com/borkdude/status/1341009566012731392/photo/1

gistfile1.txt

(defn slow-assoc [m & [k v & kvs :as dat]]
  (if (empty? dat)
    m
    (apply slow-assoc (assoc m k v) kvs)))

(defn emit-assoc [ [ksym vsym]]
  `(assoc  ~ksym ~vsym))

(defmacro fast-assoc [msym & kvsyms]
  (let [assocs (map #(emit-assoc %) 
                    (partition 2 kvsyms))]
    `(-> ~msym ~@assocs)))

(defn test-assoc [assoc-impl]
  (time (dotimes [_ 10000000]
          (assoc-impl {} :k1 :v1 :k2 :v2 :k3 :v3))))


(def fast-assoc-macro-wrapper #(fast-assoc {} :k1 :v1 :k2 :v2 :k3 :v3))

(defn test-fast-assoc-fn []
  (time (dotimes [_ 10000000]
          (fast-assoc-macro-wrapper))))


;; TESTS

(test-assoc assoc)
;; "Elapsed time: 2030.44051 msecs"
;; nil

(test-assoc slow-assoc)
;; "Elapsed time: 5497.855402 msecs"
;; nil

(test-fast-assoc-fn)
;; "Elapsed time: 1079.879993 msecs"
nil