[ruby-core:107248] [Ruby master Feature#18273] Class#subclasses

Issue #18273 has been updated by fxn (Xavier Noria).


> This is perfectly fine, Ruby isn't concerned about wether a Class is still present in the constant table or not

I am talking about object lifetimes, my example does not store the class object in a constant.

In my view, this API is not consistent with the Ruby model. In the Ruby model, you have class objects, and they have superclasses. Instances hold a strong reference to their classes.

Whether you store those objects in variables or constants, or not at all (as in the example above), is orthogonal to that model.

So, in this model, `Class#subclasses` cannot be deterministic.

----------------------------------------
Feature #18273: Class#subclasses
https://bugs.ruby-lang.org/issues/18273#change-96109

* Author: byroot (Jean Boussier)
* Status: Closed
* Priority: Normal
----------------------------------------
Ref: https://github.com/rails/rails/pull/43481

Something we forgot to mention in [Feature #14394], is either a parameter or another method to only get direct descendants.

Active Support has been offering `Class.subclasses` as:

```ruby
  def subclasses
    descendants.select { |descendant| descendant.superclass == self }
  end
```

It seems a bit silly to grab all descendants and then restrict the list when `Class#descendants` had to do some recursion to get them all in the first place.

### Proposal

We could either implement `Class#subclasses` directly, or accept a parameter in `Class#descendants`, e.g. `descendants(immediate = false)`.

cc @eregon



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