Implementing an Event Dispatcher in PHP

An event dispatcher sends named events to registered handlers without tight direct dependencies.

What It Does

An event dispatcher sends named events to registered handlers without tight direct dependencies. The following examples distinguish a normal use case, a boundary case and a practical application.

Requirements and Compatibility

PHP 8.x and a local test environment. Apply input validation, correct error handling and the requirements of any optional libraries.

The code focuses on the core concept. Production implementation may also need routes, validation, persistence, authorization or deployment tooling.

Example 1: Basic Behavior

Understand the primary operation and its inputs.

<?php
$listeners = ['saved' => [fn ($id) => print('saved:' . $id)]];
foreach ($listeners['saved'] as $listener) $listener(8);

Example 2: Another Case

Check failure behavior or a different execution path.

<?php
$events = [];
$subscribe = function (string $event, Closure $fn) use (&$events): void { $events[$event][] = $fn; };
$subscribe('updated', fn (array $data) => print($data['id']));
foreach ($events['updated'] as $listener) $listener(['id' => 'p9']);

Practical Example: Putting It to Use

Apply the behavior in a small, controlled scenario.

<?php
class EventBus { private array $handlers = []; public function on(string $name, Closure $handler): void { $this->handlers[$name][] = $handler; } public function emit(string $name, mixed $data): void { foreach ($this->handlers[$name] ?? [] as $handler) $handler($data); } }
$bus = new EventBus(); $bus->on('order', fn ($id) => print($id)); $bus->emit('order', 12);

Important Behavior and Edge Cases

Event ordering and failure handling should be explicit; in-process dispatch is not a durable queue.

Comparison with Related Functions or Approaches

Common Beginner Mistakes

Key Takeaways

• An event dispatcher sends named events to registered handlers without tight direct dependencies.
• Event ordering and failure handling should be explicit; in-process dispatch is not a durable queue.
• Use a message broker for retryable asynchronous processing.

Before adapting these examples, verify the return values, test the failure paths and confirm that your application meets its security and environment requirements.