`update-vals` not preserving sorted maps?

Wed, 27 Jul 2022 08:35:05 +0000

Hello! We recently found that when applying update-vals to a sorted map, it's converted back into an unsorted array/hash map due to the collection not being transientable. Example given below. As a note, this differs from medley/map-vals which preserves sorting and which we were using for this functionality previously to 1.11.

Is this intended behavior? If so, I'd be curious about the intent behind it :) Thanks!

user> (def m (sorted-map :a 0 :b 0))
;; => #'user/m
user> (type m)
;; => clojure.lang.PersistentTreeMap
user> (type (update-vals m inc))
;; => clojure.lang.PersistentArrayMap
user> (type (medley.core/map-vals inc m))
;; => clojure.lang.PersistentTreeMap

Bug when using nested sorted maps

Fri, 26 Mar 2021 08:47:17 +0000

After discussing it on Slack, the following definitely feels like a bug. At the very least, it throws weirdly in CLJS while it is perfectly (and intuitively) fine in Clojure JVM.

(def tree
     (sorted-map 3
                 (sorted-map 1
                             {:a 'leaf-A})))
(def subtree
     (sorted-map 1
                 (sorted-map 100
                             {:b 'leaf-B})))
;; Fine, of course, but now...
(assoc tree
       3
       subtree)
;; Throws:   Error: Cannot compare :a to 100

Andy Fingerhut pointed to a difference in implementation. Clojure compares by reference and CLJS by value, forcing a deep comparison. Even then, I find the error cryptic and argue that logically speaking, Clojure makes sense.

Citing him, Clojure implementation:

https://github.com/clojure/clojure/blob/master/src/jvm/clojure/lang/PersistentTreeMap.java#L132

And CLJS implementation:

https://github.com/clojure/clojurescript/blob/master/src/main/cljs/cljs/core.cljs#L8857

Is there something we didn't see?

Clojure Q&A - Recent questions tagged sorted-map

`update-vals` not preserving sorted maps?

Bug when using nested sorted maps