We're updating the issue view to help you get more done. 

empty? is broken for transient collections

Description

Couldn't find whether it was brought up earlier, but it seems that empty? predicate is broken for transient collections

1 2 3 4 5 6 7 8 user=> (empty? (transient [])) IllegalArgumentException Don't know how to create ISeq from: clojure.lang.PersistentVector$TransientVector clojure.lang.RT.seqFrom (RT.java:528) user=> (empty? (transient {})) IllegalArgumentException Don't know how to create ISeq from: clojure.lang.PersistentArrayMap$TransientArrayMap clojure.lang.RT.seqFrom (RT.java:528) user=> (empty? (transient #{})) IllegalArgumentException Don't know how to create ISeq from: clojure.lang.PersistentHashSet$TransientHashSet clojure.lang.RT.seqFrom (RT.java:528)

The workaround is to use (zero? (count (transient ...))) check instead.

Cause: empty? is based on seqability, which transients don't implement.

Proposed Add a branch to empty? for counted? colls. Transients implement Counted so gain support via this branch. Other colls that are counted are faster. Seq branch continues to work for seqs.

Perf test:

1 2 3 4 5 6 7 8 9 10 (def p []) (def p1 [1]) (def t (transient [])) (def t1 (transient [1])) ;; take last time of all these (dotimes [i 20] (time (dotimes [_ 10000] (empty? p)))) (dotimes [i 20] (time (dotimes [_ 10000] (empty? p1)))) (dotimes [i 20] (time (dotimes [_ 10000] (empty? t)))) (dotimes [i 20] (time (dotimes [_ 10000] (empty? t1))))

Results:

coll

before

after

result

p

0.72 ms

0.08 ms

much faster when empty

p1

0.15 ms

0.13 ms

slightly faster when not empty

t

error

0.19 ms

no longer errors

t1

error

0.20 ms

no longer errors

Not sure if doc string should be tweaked to be more generic, particularly the "same as (not (seq coll))" which is now only true for Seqable but not Counted. I think the advise to use (seq coll) for seq checks is still good there.

I did a skim for other types that are Counted but not seqs/Seqable and didn't find much other than internal things like ChunkBuffer. Many are both and would thus use the counted path instead (all the persistent colls for example and any kind of IndexedSeq).

I guess another option would be just to fully switch empty? to be about (zero? (bounded-count 1 coll)) and lean on count's polymorphism completely.

Patch: clj-1872.patch

Environment

None

Status

Assignee

Unassigned

Reporter

import

Labels

Approval

Vetted

Patch

Code and Test

Fix versions

Affects versions

Release 1.7

Priority

Critical