Redefining Further - "Redefining the Service Layer with Groovy Categories"

Service.groovy

class LocalPaymentService implements PaymentService {

  	public String process(PaymentType paymentType) {
		if (paymentType instanceof CreditCardPaymentType) {
			use (CreditCardPaymentProcessor) {
				return paymentType.process()
			}
		}
		// ...
	}

}