code: func (d Delivery) Ack(multiple bool) error {
  	if d.Acknowledger == nil {
  		return errDeliveryNotInitialized
  	}
  	return d.Acknowledger.Ack(d.DeliveryTag, multiple)
  }
docs: /*
  Ack delegates an acknowledgement through the Acknowledger interface that the
  client or server has finished work on a delivery.
  
  All deliveries in AMQP must be acknowledged.  If you called Channel.Consume
  with autoAck true then the server will be automatically ack each message and
  this method should not be called.  Otherwise, you must call Delivery.Ack after
  you have successfully processed this delivery.
  
  When multiple is true, this delivery and all prior unacknowledged deliveries
  on the same channel will be acknowledged.  This is useful for batch processing
  of deliveries.
  
  An error will indicate that the acknowledge could not be delivered to the
  channel it was sent from.
  
  Either Delivery.Ack, Delivery.Reject or Delivery.Nack must be called for every
  delivery that is not automatically acknowledged.
  */