Listing all subclasses of a class, excluding the class itself. This is useful for listing all Models of a database adapter, such as Ohm::Model.subclasses and ActiveRecord::Base.subclasses .

subclasses.rb

class Class
  def subclasses
    class_hash = {}
    ObjectSpace.each_object do |obj|
      if Class == obj.class
        # remove first item from ancestors, which is the class itself - it's wrong to say a class is a subclass of itself
        if obj.ancestors[1..-1].include? self
          class_hash[obj] = true
        end
      end
    end
    class_hash.keys
  end
end