HTTP/2 200 x-amz-id-2: VoNagCp1CZesUfCdyG+1OS1ee2dA/n/aDgRDH/6/GCA6RjmuoLDHSIGtNFVlFWlVYF9OyHr3lkjZLwsufZGR+UqCPKOG0lsbyNkQTOY/gks= x-amz-request-id: 80GXFFCYVCHWK6TZ last-modified: Tue, 27 May 2025 06:51:22 GMT etag: "36cfa31ac1e4202297fdd37b74334a7b" x-amz-server-side-encryption: AES256 server: AmazonS3 content-encoding: gzip via: 1.1 varnish, 1.1 varnish content-type: text/plain; charset=utf-8 accept-ranges: bytes age: 0 date: Fri, 25 Jul 2025 18:35:07 GMT x-served-by: cache-tyo11943-TYO, cache-bom-vanm7210087-BOM x-cache: MISS, MISS x-cache-hits: 0, 0 x-timer: S1753468507.729463,VS0,VE382 vary: Accept-Encoding content-length: 1082 From: "Ethan (Ethan -) via ruby-core" Date: 2025-05-27T06:47:45+00:00 Subject: [ruby-core:122305] [Ruby Bug#21376] Inconsistent equality between Sets with different compare_by_identity, different classes Issue #21376 has been reported by Ethan (Ethan -). ---------------------------------------- Bug #21376: Inconsistent equality between Sets with different compare_by_identity, different classes https://bugs.ruby-lang.org/issues/21376 * Author: Ethan (Ethan -) * Status: Open * ruby -v: ruby 3.5.0dev (2025-05-26T17:42:35Z master 909a0daab6) +PRISM [x86_64-darwin22] * Backport: 3.2: UNKNOWN, 3.3: UNKNOWN, 3.4: UNKNOWN ---------------------------------------- This is an inconsistency between the new core Set and the ruby-implemented Set. I think probably the new implementation's behavior seems correct and the ruby implementation is an incorrect edge case. ```ruby class MySet < Set end o = Object.new Set.new([o]).compare_by_identity == MySet.new([o]) # => false on 3.5.0; true with the ruby implementation ``` My understanding is that, for Hash, if two hashes have unequal `compare_by_identity?` they are never equal (even if containing identical contents), unless both are empty. It would make sense for Set to be the same. Hmm, analyzing the ruby Set#== a bit more, I see a further edge case where a non-identity set is considered equal to an identity set with as few as one element in common. ```ruby set_by_eq = Set.new(['a', 'b', 'c']) # => # set_by_id = MySet.new.compare_by_identity.merge(['a', 'a'.dup, 'a'.dup]) # => # set_by_eq == set_by_id # => true in the ruby set, false in core set set_by_id == set_by_eq # => false in both ``` The latter seems unlikely it would ever be triggered unintentionally. The former I did happen across, but since I think the new behavior is correct, I will not be affected when I fix my code to consistently compare_by_identity. Given that, it may be questionable whether it's worth fixing. -- https://bugs.ruby-lang.org/ ______________________________________________ ruby-core mailing list -- ruby-core@ml.ruby-lang.org To unsubscribe send an email to ruby-core-leave@ml.ruby-lang.org ruby-core info -- https://ml.ruby-lang.org/mailman3/lists/ruby-core.ml.ruby-lang.org/