Sharing a value slot across multiple objects.

thing.rb

class Thing
  @@things = {}

  def initialize
    @pointer = self.hash
  end

  def set(x)
    @@things[@pointer] = x
  end

  def get
    @@things[@pointer]
  end

  def merge(thing2)
    set(thing2.get)
    thing2.pointer = @pointer
  end

  def pointer=(p)
    @pointer = p
  end
end

thing_spec.rb

require 'thing'

describe Thing do

  before(:all) do
    @t1 = Thing.new
    @o1 = Object.new
    @t2 = Thing.new
    @o2 = Object.new

    @t1.set(@o1)
    @t2.set(@o2)

    @t3 = Thing.new
    @t3.set(Object.new)
    @t4 = Thing.new
    @t4.set(Object.new)
  end

  it "should return the same thing from get that was passed to set" do
    @t1.get.should == @o1
    @t2.get.should == @o2
  end

  it "should merge values from one thing to another" do
    @t1.merge(@t2)
    @t1.get.should == @t2.get
    @t1.get.should == @o2
  end

  it "should merge values across three things" do
    @t2.merge(@t3)
    @t2.get.should == @t3.get
    @t1.get.should == @t2.get
    @t1.get.should == @t3.get
  end

  it "should merge values across four things" do
    @t1.merge(@t4)
    @t1.get.should == @t2.get
    @t2.get.should == @t3.get
    @t3.get.should == @t4.get
  end

end