I want to pass a java method call to a function. So instead of this:
(defn call-method []
(.getCanonicalName Object))
I have something like this...
(defn indirect-call [f clazz]
(f clazz))
(defn indirect-call-memfn []
(indirect-call (memfn ^java.lang.Class getCanonicalName) Object))
(defn indirect-call-anon []
(indirect-call #(.getCanonicalName ^java.lang.Class %) Object))
I am not sure which is faster yet, but either should work. But,
performance-wise I am creating a new function for every call (the
anonymous function) when I only ever need one. Which isn't idea.
One solution would be this:
(def indirect-call-memfn-cached
(let [f (memfn ^java.lang.Class getCanonicalName)]
(fn []
(indirect-call f Object))))
(def indirect-call-anon-cached
(let [f #(.getCanonicalName ^java.lang.Class %)]
(fn []
(indirect-call f Object))))
Or, if I want to stay using defn the slightly evil looking:
(let [f #(.getCanonicalName ^java.lang.Class %)]
(defn indirect-call-defn-anon-cached[]
(indirect-call f Object)))
Which seems to work, but is fairly horrible syntactically.
I have thought about writing a macro which I might call "one-fn" which
looks like fn but caches. The best I have come up with is to turn the
contents of the &form variable into a hash, and store the functions in
global state. So something like this...
(one-fn [x] (.getCanonicalName x))
At run time we would have something like
(if-let [f (get &one-fn-state 423432423)]
f
(let [r (fn [x] (.getCanonicalName x))]
(swap! one-fn-state assoc 423432423 r)
r))
I can see some nasty edge cases where this will break, of course. But
most of all, I wonder whether I am missing something obvious that would
be far better. In the ideal world, I'd like one-fn to affect the
compiled code, so that a single instance is shared, but I can't see a
way to achieve this.
Thoughts? Has it already been done?
Phil
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