I'm wondering what everyone thinks of using closures to mimic a simplistic
object system in Clojure? I'm not sure what to think of it yet, but the
idea is that you wrap object fields inside a closed function, and it
returns a map of methods that operates over those fields.
Here's an example of using this pattern to implement a StopWatch:
(import [java.lang System])
(defn new-stopwatch []
(let [start-time (atom nil)
elapsed (atom 0)]
{:start (fn []
(when (nil? @start-time)
(reset! start-time (System/currentTimeMillis))))
:stop (fn []
(when-not (nil? @start-time)
(reset! elapsed
(+ @elapsed
(- (System/currentTimeMillis) @start-time)))
(reset! start-time nil))
@elapsed)
:reset (fn []
(reset! start-time nil)
(reset! elapsed 0)
@elapsed)
:elapsed (fn []
(if-not (nil? @start-time)
(- (System/currentTimeMillis) @start-time)
@elapsed))}))
(let [sw1 (new-stopwatch)
sw2 (new-stopwatch)]
((:start sw1))
((:start sw2))
(Thread/sleep 100)
((:reset sw1))
((:start sw1))
(println (str "Elapsed for SW1: " ((:elapsed sw1))))
(println (str "Elapsed for SW2: " ((:elapsed sw2))))
(Thread/sleep 100)
(println (str "SW1: " ((:stop sw1))))
(println (str "SW2: " ((:stop sw2)))))
I find for certain things, like a stopwatch, this pattern is actually
pretty nice. I can't think of any alternative way to do this in Clojure
that I'd like better actually.
What are your thoughts?
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