Ruby 3.1 introduces the Class#subclasses method which returns all classes directly inheriting from the receiver without including singleton classes.
We can see many implementations for calculating all subclasses of a particular class from the Ruby community with different gems. The ActiveSupport::DescendantsTracker is one of such implementations used in Rails framework. Finally, Ruby has added the Class#subclasses native implementation for it's 3.1 version release.
After Ruby 3.1
1=> class User; end 2=> class Employee < User; end 3=> class Client < User; end 4 5=> class Manager < Employee; end 6=> class Developer < Employee; end 7 8=> User.subclasses 9=> [Employee, Client] 10 11=> Employee.subclasses 12=> [Manager, Developer] 13 14=> Developer.subclasses 15=>