Clojure extend Assotiative arity

Question

I need to implement custom assoc, but it does not work with multiple arguments. It processes only first pair. It seems that it calls assoc directly, not via core assoc and then RT/assoc.

(def my-assoc (reify
                clojure.lang.Associative
                  (assoc [_ k v]
                    (println "assoc!!" k v))))

(assoc my-assoc :a 2 :b 3) ;; prints only :a 2

How it should be done to support multi arity?

score 3 · Accepted Answer · answered Jun 17 '17 at 11:22

3

println returns nil. So return the original value:

(def my-assoc (reify
                clojure.lang.Associative
                (assoc [m k v]
                  (println "assoc!!" k v)
                  m)))

(assoc my-assoc :a 2 :b 3) ;; prints both

answered Jun 17 '17 at 11:22

ClojureMostly

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If you look at [the source for `clojure.core/assoc`](https://github.com/clojure/clojure/blob/clojure-1.9.0-alpha14/src/clj/clojure/core.clj#L181), you'll see that it cascades calls to `RT/assoc` for each `k v` pair. – Thumbnail Jun 17 '17 at 21:06

Clojure extend Assotiative arity

1 Answers1