[ruby-core:122456] [Ruby Bug#21396] Set#initialize should call Set#add on items passed in

5 Jun 2025

      ...
ruby -v test.rb
ruby 3.4.1 (2024-12-25 revision 48d4efcb85) +PRISM [arm64-darwin24]
#<Foo: {3}>
Issue #21396 has been updated by knu (Akinori MUSHA).

I've always created custom variants of Set too, and I don't think it's rare to find these in in-house codebases.

----------------------------------------
Bug #21396: Set#initialize should call Set#add on items passed in
https://bugs.ruby-lang.org/issues/21396#change-113645

* Author: tenderlovemaking (Aaron Patterson)
* Status: Open
* Backport: 3.2: UNKNOWN, 3.3: UNKNOWN, 3.4: UNKNOWN
----------------------------------------
```ruby
class Foo < Set
  def add(item) = super(item.bytesize)
end

x = Foo.new(["foo"])
p x
p x.include?(3)
```

On Ruby 3.4 the output is this:

```
true
```

On Ruby master the output is this:

```
...
make run
./miniruby -I./lib -I. -I.ext/common  -r./arm64-darwin24-fake  ./test.rb 
#<Set: {"foo"}>
false

The bug is that `initialize` is not calling `add` for the elements passed in, so the subclass doesn't get a chance to change them.

I've sent a PR here: https://github.com/ruby/ruby/pull/13518

-- 
https://bugs.ruby-lang.org/