Following up on the thread about the massive overhead of String, I tried
writing a string collection type that stores strings as bytes, converting
to String on-demand. It seems to work. Memory footprint and performance are
good for the application.
The hard part was trying to track down the correct interfaces and
invocations. I note that "Clojure Programming" makes the same observation
in the section about clojure abstractions: "such things are largely
undocumented". I guess this situation hasn't improved? I had to proceed
mostly by experimentation, and am still unclear on, for example, why I
needed to use an interop call in some places (like cons), but should not in
others.
Would be happy for any feedback on this attempt:
(deftype StringVec [pv]
clojure.lang.IPersistentVector
(seq [self] (map #(String. ^bytes %) pv))
(nth [self i] (String. ^bytes (.nth ^clojure.lang.IPersistentVector pv
i)))
(nth [self i notfound] (String. ^bytes (.nth
^clojure.lang.IPersistentVector pv i (.getBytes ^String notfound))))
clojure.lang.ILookup
(valAt [self i] (when-let [res (.valAt ^clojure.lang.IPersistentVector pv
i)]
(String. ^bytes res)))
(valAt [self i notfound] (String. ^bytes (.valAt
^clojure.lang.IPersistentVector pv i (.getBytes ^String notfound))))
clojure.lang.ISeq
(first [self] (String. ^bytes (first pv)))
(next [self] (->StringVec (next pv)))
(more [self] (->StringVec (rest pv)))
(cons [self s] (->StringVec (.cons ^clojure.lang.IPersistentVector pv
(.getBytes ^String s))))
(count [self] (count pv))
Object
(toString [self] (str (into [] self))))
(defn stringvec [coll]
(into (->StringVec []) coll))
(defmethod print-method StringVec [v, ^java.io.Writer w]
(.write w (.toString ^StringVec v)))
Speak of cons, I gather ISeq cons is unrelated to cons, the function, but
rather is required for conj?
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