From: "Eregon (Benoit Daloze) via ruby-core" <ruby-core@...>
Date: 2025-11-17T09:22:18+00:00
Subject: [ruby-core:123826] [Ruby Bug#21375] Set[] does not call #initialize

Issue #21375 has been updated by Eregon (Benoit Daloze).


I should also mention for the concurrent-ruby case that using `::Set` on Ruby 4+ is not an option because it's not thread-safe enough:
https://github.com/ruby-concurrency/concurrent-ruby/issues/1093#issuecomment-3540742547

----------------------------------------
Bug #21375: Set[] does not call #initialize
https://bugs.ruby-lang.org/issues/21375#change-115229

* 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
```



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