Hello everybody,
Recently I was implementing Insertion Sort in Clojure and did that using
transients:
--- cut ---
(defn- insert
"Insert element from `idx` into correct position in transient vector
`tv`."
[tv idx]
(let [current-value (get tv idx)]
(loop [i idx v tv]
(let [left-value (get v (dec i))]
(if (and (pos? i)
(> left-value current-value))
(recur (dec i) (assoc! v i left-value))
(assoc! v i current-value))))))
(defn insertion-sort
"Insertion sort using transients."
[v]
(let [size (-> v count dec)]
(loop [i 1 tv (transient v)]
(if (<= i size)
(recur (inc i) (insert tv i))
(persistent! tv)))))
--- cut ---
And have a few questions/concerns:
1. IIUC transients are for this purpose - to do controlled performance
optimizations, right?
2. Imperative insertion sort has O(1) space requirement. Does transients
version have the same property?
3. I read that transients should not be bashed in place, but have seen the
following code, which seems to be only to be able to "bash in place":
(let [tv (atom (transient v))]
(doseq [exrps]
(reset! tv (assoc! tv k v)))
(persistent! tv))
Is this approach idiomatic or should be avoided? To me it looks strange. My
approach is to write non-transient version, then just add transient, ! to
mutators, and persist result.
Thank you,
Przemysław
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