module MemberEquivalence
  def ==(o)
    _true_for_all_instance_variables(:==, o)
  end

  def eql?(o)
    _true_for_all_instance_variables(:eql?, o)
  end

  def _true_for_all_instance_variables(operator, other_object)
    instance_variables.each { |var|
      return false unless instance_variable_get(var).send(operator,
        other_object.instance_variable_get(var))
    }
    true
  end

  def hash
    instance_variables.inject(0) { |hash, var|
        hash.hash ^ instance_variable_get(var).hash }
  end
end