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


> In the sense that, as a programmer, if I do not change the collection, it should stay the same.

Of course, removing a subclass is ill-defined and that is the root problem I see here. And in Ruby that makes sense, because the link only went upwards only.

On the other hand, `Module#ancestors` can be a linearized cache because there is no API or way to remove ancestors.

Ruby doesn't have API/semantics to provide a similar `Class#subclasses`.

----------------------------------------
Feature #18273: Class#subclasses
https://bugs.ruby-lang.org/issues/18273#change-96124

* 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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