Fragility - "Redefining the Service Layer with Groovy Categories"

Service.groovy

class LocalPaymentService implements PaymentService {
  
	// Dependency injected from container
	CreditCardPaymentGateway creditCardPaymentGateway
	GiftCardPaymentGateway giftCardPaymentGateway
	CheckPaymentGateway checkPaymentGateway
	EmployeePaymentGateway employeePaymentGateway

	public String process(PaymentType paymentType) throws IllegalArgumentException {
		if (paymentType instanceof CreditCardPaymentType) {
			if ("CA".equalsIgnoreCase(paymentType.getPayee().getBillingAddress().getState())) {
				return doCaliforniaCreditProcessing(paymentType)
			} 
			return doProcess(paymentType)
		} else if (paymentType instanceof GiftCardPaymentType) {
			return doProcess(paymentType)
		} else if (paymentType instanceof CheckPaymentType) {
			return doProcess(paymentType)
		} else if (paymentType instanceof EmployeePaymentType) {
			return doProcess(paymentType)
		}
		throw new IllegalArgumentException("Supplied payment type is not supported.");
	}

	// … [snip] … implementation methods

}