[ruby-core:122412] [Ruby Bug#21396] Set#initialize should call Set#add on items passed in

Issue #21396 has been updated by jeremyevans0 (Jeremy Evans).


This is not a bug, IMO.  Using underlying functions instead of calling methods was one of the deliberate design decisions for core Set (see #21216), and how other core collection classes work. `Array.new(1, true)` does not call `Array#[]=`, it calls `rb_ary_store`.  

If we want to do this for `Set#initialize` and `Set.[]` for backwards compatibility, we should be consistent and call methods instead of underlying functions for every case where the methods were called in stdlib set.  That will make it slower, though.

FWIW, in the code path you are using in stdlib Set, `Set#add` is not called directly, you are relying on `Set#merge` calling it.  So this is at least a request to have `Set#initialize` call `Set#merge` and to have `Set#merge` call `Set#add` for every element.

----------------------------------------
Bug #21396: Set#initialize should call Set#add on items passed in
https://bugs.ruby-lang.org/issues/21396#change-113592

* 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:

```
> ruby -v test.rb
ruby 3.4.1 (2024-12-25 revision 48d4efcb85) +PRISM [arm64-darwin24]
#<Foo: {3}>
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



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