EventDispatcher: 결합도가 낮은 이벤트

$ composer require symfony/event-dispatcher

<?php
use Symfony\Contracts\EventDispatcher\Event;

class UserRegisteredEvent extends Event
{
    public const NAME = "user.registered";

    public function __construct(public readonly User $user) {}
}

<?php
class SendWelcomeEmailListener
{
    public function __invoke(UserRegisteredEvent $event): void
    {
        mail($event->user->email, "Welcome!", "Thanks for joining!");
    }
}

<?php
use Symfony\Component\EventDispatcher\EventDispatcher;

$dispatcher = new EventDispatcher();
$dispatcher->addListener(
    UserRegisteredEvent::NAME,
    new SendWelcomeEmailListener()
);

<?php
$user = new User("alice@example.com");
$dispatcher->dispatch(new UserRegisteredEvent($user), UserRegisteredEvent::NAME);

<?php
$dispatcher->addListener("user.registered", $logListener, 10);   // runs first
$dispatcher->addListener("user.registered", $emailListener, 0);  // runs second

<?php
use Symfony\Component\EventDispatcher\EventSubscriberInterface;

class UserSubscriber implements EventSubscriberInterface
{
    public static function getSubscribedEvents(): array {
        return [
            UserRegisteredEvent::NAME => "onUserRegistered",
        ];
    }

    public function onUserRegistered(UserRegisteredEvent $event): void {
        // ...
    }
}