Template Method and Pluggable Strategies

Keep core flows stable; enable extension via small classes.

Template Method

Use a base class that defines the algorithm skeleton; subclasses override hooks.

abstract class Importer { final public function handle(string $path): void { $rows = $this->load($path); $data = $this->normalize($rows); $this->validate($data); $this->save($data); } abstract protected function load(string $path): array; protected function normalize(array $rows): array { return $rows; } protected function validate(array $data): void {} abstract protected function save(array $data): void; }

Strategy/Plugin

Define an interface; register implementations; select by key/config.

interface PaymentGateway { public function charge(int $cents, string $currency): string; }

final class StripeGateway implements PaymentGateway { /* ... / } final class BraintreeGateway implements PaymentGateway { / ... */ }

final class PaymentsRegistry { /** @param array<string,PaymentGateway> $drivers */ public function __construct(private array $drivers) {} public function for(string $key): PaymentGateway { return $this->drivers[$key]; } }

Prefer adding a class over editing switch statements. Test implementations in isolation.