Issue #21375 has been updated by Eregon (Benoit Daloze). IMO this is unnecessarily breaking compatibility. If we don't want to support subclasses of Set properly as it used to work (and calling `initialize` is I think a totally reasonable assumption, especially for any library which used to be written in Ruby), then I think we should forbid subclassing Set entirely to make it clear. ---------------------------------------- Bug #21375: Set[] does not call #initialize https://bugs.ruby-lang.org/issues/21375#change-113509 * 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 ---------------------------------------- I have a subclass of Set that overrides #initialize. Following #21216, .new does call #initialize but .[] does not. ```ruby class MySet < Set def initialize(enum = nil) compare_by_identity super end end MySet.new.compare_by_identity? # => true MySet[].compare_by_identity? # => false ``` -- https://bugs.ruby-lang.org/