On Thu, Jul 9, 2009 at 7:56 PM, Conrad<drc...@gmail.com> wrote:
>
> I'm trying to optimize an inner loop and need a variable that mutates
> to make this work. It does NOT need to be a thread-safe variable.
> What's the best way to create a "plain ol' mutating variable" in
> Clojure? I know I can always use an Atom, but I was wondering if
> there's a more low-level way (besides using the java interop, since I
> may still want this variable to be dynamically typed.)
You can try with-local-vars. I'm not sure of the performance
characteristics of this versus using an atom, but it certainly feels
more imperative:
user=> (doc with-local-vars)
-------------------------
clojure.core/with-local-vars
([name-vals-vec & body])
Macro
varbinding=> symbol init-expr
Executes the exprs in a context in which the symbols are bound to
vars with per-thread bindings to the init-exprs. The symbols refer
to the var objects themselves, and must be accessed with var-get and
var-set
nil
user=> (with-local-vars [i 0 j 0]
(doseq [k (range 10)]
(println "i * j =" (* (var-get i) (var-get j)))
(var-set i (inc (var-get i)))
(var-set j (dec (var-get j)))))
i * j = 0
i * j = -1
i * j = -4
i * j = -9
i * j = -16
i * j = -25
i * j = -36
i * j = -49
i * j = -64
i * j = -81
nil
HTH,
- J.
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