gistfile1.rbx

class Ancestor
  attr_accessor :id

  def initialize(id)
    @id = id
  end

  def ==(other)
    id == other.id
  end
end
class Foo < Ancestor
  def initialize(id)
    @id = id
  end
end
class Bar < Ancestor
  include Comparable
end
Foo.new(1) == Foo.new(1)
Bar.new(1) == Bar.new(1)