Steve Losh posted the following Clojure snippet : ; Integers and Longs are equal.

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Asked: June 14, 20262026-06-14T04:29:58+00:00 2026-06-14T04:29:58+00:00

Steve Losh posted the following Clojure snippet : ; Integers and Longs are equal.

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Steve Losh posted the following Clojure snippet:

; Integers and Longs are equal.
(= (Integer. 1) (Long. 1))
true

; Even negative ones.
(= (Integer. -1) (Long. -1))
true

; When you use them as keys in maps, the maps are still equal.
(= {(Integer. 1) :foo} {(Long. 1) :foo})
true

(= {(Integer. -1) :foo} {(Long. -1) :foo})
true

; When you use positive numbers as keys to sets, they're also equal.
(= #{(Integer. 1)} #{(Long. 1)})
true

; But negative ones aren't. But only in sets. Maps are fine. lol.
(= #{(Integer. -1)} #{(Long. -1)})
false

What is the reason for this behavior? Is it considered a defect or is there a “formal logic” / set theory reason why (Integer. -1) not equaling (Long. -1) in a persistent set?