Demonstration of shallow copy

dup.rb

require 'pp'

class DupMe
  attr_accessor :stuff
  def initialize
    @stuff=[1,2,3,4,5,6]
  end

  def copy
    new = self.dup
    new.stuff=@stuff.dup
    new
  end
end

original = DupMe.new
dupped = original.dup
copied = original.copy

dupped.stuff.pop

pp original.stuff
pp dupped.stuff
pp copied.stuff
puts


dupped.stuff = "hello"
copied.stuff = "I'm a copy"

pp original.stuff
pp dupped.stuff
pp copied.stuff

initialize_copy.rb

require 'pp'

class DupMe
  attr_accessor :stuff
  def initialize
    @stuff=[1,2,3,4,5,6]
  end

  def initialize_copy(source)
    @stuff=stuff.dup
  end

  def copy
    new = self.dup
    new.stuff=@stuff.dup
    new
  end
end

original = DupMe.new
dupped = original.dup
copied = original.copy

dupped.stuff.pop

pp original.stuff
pp dupped.stuff
pp copied.stuff
puts


dupped.stuff = "hello"
copied.stuff = "I'm a copy"

pp original.stuff
pp dupped.stuff
pp copied.stuff