Memento パターン

#!/usr/bin/env ruby -KU

require 'rubygems'
require 'spec'

class Originator
  class Memento
    def initialize(state)
      # Originator の元の状態を壊しても、この Memento オブジェクトが初回以降の restore で
      # 破壊されないよう dup が必要
      @state = state.dup
    end
    
    def state
      # Originator の元の状態を壊しても、この Memento オブジェクトが二度目の restore で
      # 破壊されないよう dup が必要
      @state.dup
    end
  end

  attr_accessor :state

  # メモリに巨大なデータが多数あり、state から再構成可能であるように見せる
  def save_to_memento
    Memento.new(@state)
  end

  def restore_from_memento(m)
    @state = m.state
  end

end

class Caretaker < Array; end

describe Originator do
  before(:all) do
    @caretaker = Caretaker.new
    @originator = Originator.new

    @originator.state = "State1"
  end

  it "should have original state" do
    @originator.state.should == 'State1'
  end

  it "should update state" do
    @originator.state = "State2"
    @originator.state.should == 'State2'
  end

  it "should save memento" do
    @caretaker << @originator.save_to_memento
    @caretaker.size.should == 1
  end

  it "should update state after save to memento" do
    @originator.state = "State3"
    @originator.state.should == 'State3'
  end

  it "should save to memento again" do
    @caretaker << @originator.save_to_memento
    @caretaker.size.should == 2
  end

  it "should update state after save to memento again" do
    @originator.state = "State4";
    @originator.state.should == 'State4'
  end

  it "should restore to original save point" do
    @originator.restore_from_memento @caretaker[0]
    @originator.state.should == 'State2'
  end

  it "should restore to second save point" do
    @originator.restore_from_memento @caretaker[1]
    @originator.state.should == 'State3'
  end

  it "should restore after pathological munging of restored state" do
    @originator.state[-1] = '5'
    @originator.state.should == 'State5'
    @originator.restore_from_memento @caretaker[1]
    @originator.state.should == 'State3'
  end
  
  it "should restore after pathological munging of original state" do
    @originator.state = "State6"
    @originator.state.should == 'State6'
    @caretaker << @originator.save_to_memento
    @originator.state[-1] = '7'
    @originator.state.should == 'State7'
    @originator.restore_from_memento @caretaker[2]
    @originator.state.should == 'State6'
  end
end