メソッドの引数は破壊しないで!!

HogeHogeTuple.rb

# coding: utf-8

class Tuple

  def initialize(*xs)
    @xs = xs
  end

  def [] *args
    @xs[*args]
  end

  def to_s
    "(%s)" % @xs.map(&:to_s).join(', ')
  end
end


class Hoge
  # 破壊可能な属性
  attr_accessor :fuga

  def to_s
    "hoge(%s)" % self.fuga
  end

  # こういう引数を破壊するメソッドやめて!!
  # def change!(hoge)
  #   tmp = self.fuga
  #   self.fuga = hoge.fuga
  #   hoge.fuga = tmp
  # end
end

class HogeHogeTuple < Tuple

  # こうしてほしい
  def change_fuga!
    tmp = self[0].fuga
    self[0].fuga = self[1].fuga
    self[1].fuga = tmp

    true
  end
end

hoge1 = Hoge.new
hoge1.fuga = 1
hoge2 = Hoge.new
hoge2.fuga = 2

HogeHogeTuple.new(hoge1, hoge2).change_fuga!