John Davidson

Message:

What is correct way to select interface implementation according to passed parameter?

Let's have following code:

interface PaymentProcessor {

  public function process(Order $order): void;

}



class CardPayment implements PaymentProcessor {}

class BankTransfer implements PaymentProcessor {}

class OrderService {

  public function __construct( // Load payment processors from DI

    private CardPayment $cardPayment,

    private BankTransfer $bankTransfer,

  ) {}



  // This is what is not clear to me

  private function getPaymentProcessor(string $paymentMethod): PaymentProcessor

  {

    return match ($paymentMethod) {

      'card' => $this->cardPayment,

      'bank' => $this->bankTransfer,

    }

  }



  public function payOrder(Order $order): void

  {

    $processor = $this->getPaymentProcessor($order->getPaymentMethod());

    $processor->process($order);

  }

}

What is not clear to me is how can I get PaymentProcessor by payment method name.

I would use code above, probably extracted to some "Factory". But according to answer at PHP - Using Interfaces, Strategy Pattern and Optional Method Parameters I am probably breaking open/close principle. Then what should be correct way?

---

My Answer:
> 'card' => $this->cardPayment,
> 'bank_transfer' => $this->bankTransfer,
> default => throw new \InvalidArgumentException('Invalid payment method'),
> };
> }

In the `getPaymentProcessor` method, you can use a `match` expression to select the appropriate implementation based on the passed parameter `paymentMethod`. This way, you can return the correct implementation of the `PaymentProcessor` interface according to the parameter value.