http://zawarstwaabstrakcji.pl/blog/2015/10/05/rozszerzanie-funkcjonalnosci-bez-wprowadzania-chaosu/

comment.php

interface UserRegistrationVerification
{
    public function execute(User $user);
}

final class NoVerification implements UserRegistrationVerification
{
    public function execute(User $user)
    {
        $user->activate();
    }
}

final class EmailVerification implements UserRegistrationVerification
{
    private $mailer;

    public function __construct(UserMailer $mailer)
    {
        $this->mailer = $mailer;
    }

    public function execute(User $user)
    {
        $this->mailer->sendActivationEmail($user);
    }
}

final class LoggingRegistrationService
{
    private $service;

    public function __construct(LoggerInterface $logger, RegistrationService $service)
    {
        $this->logger = $logger;
        $this->service = $service;
    }

    public function register(array $data, UserRegistrationVerification $verification)
    {
        $this->service->register($data, $verification);

        $this->logger->info(
            sprintf("User account with email \"%s\" was successfully registered.", (string) $user->getEmail())
        );
    }
}

final class RegistrationService
{
    private $users;

    private $userFactory;

    public function __construct(UserRepository $users, UserFactory $factory)
    {
        $this->users = $users;
        $this->userFactory = $factory;
    }

    public function register(array $data, UserRegistrationVerification $verification)
    {
        $user = $this->userFactory->createUser($data);
        $this->users->add($user);
        $verification->execute($user);
    }
}