iterator.rb

  class SerialNumberGenerator
    LABELS_PER_SERIAL_NUMBER = 2
    protected
      attr_accessor :serial_number_counter
    public
    
    def initialize(start:)
      self.serial_number_counter = start.to_i
    end
    def next()
      sn = self.serial_number_counter.to_s.rjust(6,"0")
      if self.serial_number_counter % LABELS_PER_SERIAL_NUMBER == 0 then
        self.serial_number_counter +=1
      end
      return sn
    end
  end