README

SuperKernel Event Dispatcher

super-kernel/event-dispatcher is the PSR-14 event dispatcher of SuperKernel: it finds the classes declared with #[Listener], creates them through the container, and calls the ones that match an event synchronously, in priority order.

Installation

composer require super-kernel/event-dispatcher

The package provides psr/event-dispatcher-implementation 1.0. It creates listeners through a PSR-11 container, super-kernel/di in a SuperKernel application, and finds them in the metadata that skernel build generates, so a project needs SKERNEL to build it.

What it provides

Psr\EventDispatcher\EventDispatcherInterface, which dispatches any event object and returns it.
Listeners declared with #[Listener] and ListenerInterface, ordered by priority.
Matching by class: a listener of a class or interface also receives its subclasses and implementations.
Stopping propagation through PSR-14's StoppableEventInterface.
Psr\EventDispatcher\ListenerProviderInterface, which lists the listeners of an event.

It does not:

dispatch asynchronously or defer events;
collect listener return values;
register or remove listeners at run time;
adapt Symfony's event dispatcher; super-kernel/framework does.

Quick start

Declare an event. Save it as src/Account/UserRegistered.php:

<?php

declare(strict_types=1);

namespace Src\Account;

final readonly class UserRegistered
{
    public function __construct(public string $email)
    {
    }
}

Declare a listener of the event. Save it as src/Account/SendWelcomeMail.php:

<?php

declare(strict_types=1);

namespace Src\Account;

use SuperKernel\Attribute\Listener;
use SuperKernel\Contract\ListenerInterface;

#[Listener]
final readonly class SendWelcomeMail implements ListenerInterface
{
    public function listen(): array
    {
        return [
            UserRegistered::class,
        ];
    }

    /**
     * @param UserRegistered $event
     */
    public function process(object $event): void
    {
        echo "Welcome mail sent to {$event->email}", PHP_EOL;
    }
}

Dispatch the event from a script. Save it as bin/register.php:

<?php

declare(strict_types=1);

use Psr\EventDispatcher\EventDispatcherInterface;
use Src\Account\UserRegistered;
use SuperKernel\Context\ApplicationContext;

require dirname(__DIR__) . '/vendor/autoload.php';

$events = ApplicationContext::getContainer()->get(EventDispatcherInterface::class);

$events->dispatch(new UserRegistered('ada@example.com'));

Build the project and run the script:

skernel build
php bin/register.php

It prints Welcome mail sent to ada@example.com.

Public surface

Name	Kind	Purpose
`SuperKernel\Attribute\Listener`	Attribute	Registers the annotated class as a listener; `priority` orders it, higher first.
`SuperKernel\Contract\ListenerInterface`	Interface	Implemented by a listener: `listen()` names its events, `process()` handles one.
`Psr\EventDispatcher\EventDispatcherInterface`	Interface	Provided by the container; dispatches an event to its listeners.
`Psr\EventDispatcher\ListenerProviderInterface`	Interface	Provided by the container; returns the listeners of an event in order.

Behavior to know

Listeners run synchronously, higher priorities first and equal priorities in the order the build found them; dispatch() returns the same event object.
A listener's exception propagates unchanged out of dispatch(), and later listeners do not run.
Every listener is created when the dispatcher is first needed. A listener that does not implement ListenerInterface, or whose listen() does not return a list of existing class or interface names, raises InvalidArgumentException then, so no event can be dispatched and skernel build fails.
Listeners are found in the build metadata: run skernel build again after adding, removing, or changing a listener, or start with skernel run, which builds first.

Documentation

The developer documentation describes declaring listeners, matching several events, stopping propagation, the listener provider, and the error messages: SuperKernel Event Dispatcher.

License

Released under the MIT License. See LICENSE.

super-kernel / event-dispatcher

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