In CLJS {{hash-ordered-coll}} and {{hash-unordered-coll}} currently consume their collections using {{seq}} instead of an iterator. Most core collection types have an efficient {{-iterator}} implementation which avoids the extra allocations inherent in {{seq}}.
Using iterators instead shows a modest performance improvement with larger collections and more frequent iterations; benchmark-runner size (1000) and repetition count (100) shows no perceptible difference on my machine (Ubuntu 18.04 using "Intel(R) Core(TM) i7-4710MQ CPU @ 2.50GHz")
`
(ns cljs.benchmark-runner
(:refer-clojure :exclude [println]))
(def println print)
(set! print-fn js/print)
;; Note that coll size and repetition count are both
;; 10x what benchmark-runner usually uses.
(def hash-coll-test
(loop [i 0 r []]
(if (< i 10000)
(recur (inc i) (conj r (str "foo" i)))
r)))
(def hash-imap-test
(loop [i 0 r {}]
(if (< i 10000)
(recur (inc i) (conj r [(keyword (str "foo" i)) i]))
r)))
(def hash-imap-int-test
(loop [i 0 r {}]
(if (< i 10000)
(recur (inc i) (conj r [i i]))
r)))
`
`
benchmark run on Ubuntu 18.04 using "Intel(R) Core(TM) i7-4710MQ CPU @ 2.50GHz"
benchmark results for master
Benchmarking with V8
[coll hash-coll-test], (hash-ordered-coll coll), 1000 runs, 1831 msecs
[coll hash-imap-test], (hash-unordered-coll coll), 1000 runs, 6506 msecs
[coll hash-imap-int-test], (hash-unordered-coll coll), 1000 runs, 8439 msecs
benchmark results with this patch
Benchmarking with V8
[coll hash-coll-test], (hash-ordered-coll coll), 1000 runs, 1629 msecs
[coll hash-imap-test], (hash-unordered-coll coll), 1000 runs, 5753 msecs
[coll hash-imap-int-test], (hash-unordered-coll coll), 1000 runs, 6810 msecs
`
