central-dispatch.md

Tricky, we can NOT:

var fxy = gen_dispatcher(fxy)
var fxy.IFn ....

Since otherwise we loose (to be tested) GCC's DCE.

Thoug this should work:

(defn create-multi-arity-fn
  []
  (fn dispatcher []
    #js[(.-cljs$lang$maxFixedArity dispatcher)
        (.-cljs$lang$fixedArities dispatcher)]))

(def foo (create-multi-arity-fn))
(set! foo -cljs$lang$maxFixedArity 2)
(set! foo -cljs$lang$fixedArities #js[0 2])
(foo)

Need to check DCE...

Measuring MFA:

    (defn set-arg-len [f]
      (set! js/yyyyyyy (.. f -cljs$core$IFn$_invoke$arity$variadic -length)))
    (defn set-mfa [f]
      (set! js/xxxxxx (.. f -cljs$lang$maxFixedArity)))

    (let [sims 4000000
          fns #js[map comp some-fn str partial vary-meta not= disj! conj assoc assoc!]
          len (alength fns)]
      (dotimes [_ 3]
        (simple-benchmark []
          (set-arg-len (aget fns (rand-int len))) sims)
        (simple-benchmark []
          (set-mfa (aget fns (rand-int len))) sims)))

Slower in Chrome by like 2x :(

Optimize for inline caches - avoid hidden classes

We could maybe get the same object layout and achieve much higher performance if we set "a few" IFn to nil on the dispatcher. To be tested!