Ruby的装饰器模式实现

class Tree
  def initialize
    puts "Make a normal tree"
  end
  def decorate
    puts "Make sure the tree won\'t fall"
  end
end
class RedBalls < Tree
  def initialize(tree)
    @parent = tree;
  end
  def decorate
    @parent.decorate
    puts "Put on some red balls"
  end
end
class BlueBalls < Tree
  def initialize(tree)
    @parent = tree;
  end
  def decorate
    @parent.decorate
    puts "Add blue balls"
  end
end
class Angel < Tree
  def initialize(tree)
    @parent = tree;
  end
  def decorate
    @parent.decorate
    puts "An angel on the top"
  end
end

tree = Angel.new(BlueBalls.new(RedBalls.new(Tree.new)))
tree.decorate