[ruby-core:126291] [Ruby Feature#9779] Add Module#descendants

6 Aug 2026

      Issue #9779 has been updated by matz (Yukihiro Matsumoto).

Accepted. Let's define `Module#descendants`.

This settles the question I left open in [#14394](https://bugs.ruby-lang.org/issues/14394#note-38). `Class#subclasses` already lets you write the transitive closure for classes in Ruby, but there is no equivalent primitive for modules, so `Module` is where this method actually adds something. Defining it there also gives `Class` the method for free.

Not including `self` is fine too. It departs from `ancestors`, but it agrees with `Class#subclasses` and with ActiveSupport's `descendants`, and `[mod, *mod.descendants]` is available when needed.

Once this is merged, I think [#14394](https://bugs.ruby-lang.org/issues/14394) can be closed.

Matz.

----------------------------------------
Feature #9779: Add Module#descendants
https://bugs.ruby-lang.org/issues/9779#change-118388

* Author: shugo (Shugo Maeda)
* Status: Open
----------------------------------------
Now classes have links to their subclasses, so how about to add Module#descendents?

```ruby
class X
end

class Y < X
end

class Z < Y
end

p X.descendents    #=> [X, Y, Z]

module A
end

module B
  include A
end

module C
  include A
end

p A.descendents    #=> [A, C, B]
```

One of my own use cases is to implement AspectJ like pointcut which matches all subclasses of the given class.

Considerations:

* Should the return value of Module#descendents include self?
* Should the return value of Module#descendents include singleton classes?

I attach a patch, where the return value includes both self and singleton classes.

---Files--------------------------------
0001-Add-Module-descendents.patch (3.75 KB)

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