I would definitely prefer clear-cached-files2. I usually use
multimethods when I need to change behavior on type of arguments, not
the argument count.
Let's take a look at reduce. I would write the shorter form in terms
of the longer one.
(defn reduce
([f coll] (reduce f (first coll) (rest coll)))
([f init coll] (reduce stuff...)))
I find that this makes my code easier to maintain.
Just my $.02
Sean
On Oct 3, 3:11 pm, Robert Stehwien <rstehw...@gmail.com> wrote:
> I'm toying around with a file utility library as part of a vow to do all my
> "scripting" in clojure so I can learn the language - this is actually my
> first attempt at writing anything "real" with clojure. I considered using
> memoize to cache file listing but wanted to be able to selectively clear the
> cache for specific file listings.
>
> I was trying to write a clear-cached-files function that would take nothing
> to clear them or take one or more items to clear that list of files. So I
> have two questions:
>
> 1) What would be the right way to call dissoc with a single item or list. I
> tried numerous things but what I have below is what I got to work and I'm
> not sure if is the best way.
>
> 2) (and the more important question). When would you prefer using a
> multimethod (clear-cached-files) that switches based on argument count or a
> single method (clear-cached-files2) with multiple argument lists?
>
> Thanks,
> Robert
>
> I put the whole source to the file utils I've written below for reference.
>
> ----------
> (ns rstehwien.clojure.fileutils
> (:gen-class)
> (:import (java.io File)))
>
> (def file-seq-cache (ref {}))
>
> (defmulti clear-cached-files (fn[& arglist] (count arglist)))
>
> (defmethod clear-cached-files 0 [& arglist]
> (dosync (alter file-seq-cache empty)))
>
> (defmethod clear-cached-files 1 [& arglist]
> (dosync (alter file-seq-cache dissoc (first arglist))))
>
> (defmethod clear-cached-files :default [& arglist]
> (doseq [arg arglist] (clear-cached-files arg)))
>
> (defn clear-cached-files2
> ([]
> (dosync (alter file-seq-cache empty)))
> ([key]
> (dosync (alter file-seq-cache dissoc key)))
> ([key & ks]
> (dosync
> (clear-cached-files2 key)
> (doseq [key2 ks] (clear-cached-files key2)))))
>
> (defn get-cached-files [path]
> (dosync
> (when-not (contains? @file-seq-cache path)
> (alter file-seq-cache conj {path (file-seq (File. path))}))
> (@file-seq-cache path)))
>
> (defn filter-files-ends-with [files suffix]
> (filter #(.. % toString (endsWith suffix)) files))
>
> (defn files-ending-with [path suffix]
> (filter-files-ends-with (get-cached-files path) suffix))
> ----------
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