def add(decorator)
      if decorators.include?(decorator)
        self.class.new(decorators)
      else
        self.class.new(decorators + [decorator])
      end
    end
def add(decorator)
      if decorators.include?(decorator)
        self.class.new(decorators)
      else
        self.class.new(decorators + [decorator])
      end
    end
Add decorator

 @api public