Equalable ruby mixin.

equalable.rb

module Equalable
  def ==(o)
    o.class == self.class && o.equality_state == equality_state
  end
  alias_method :eql?, :==

  def hash
    equality_state.hash
  end
end

class Foo
  private

  def equality_state
    [ id, name, created_at ]
  end
end