WithEvents.php

<?php

trait WithEvents
{
    private $eventHandlers;

    public function on(string $event, callable $handler): self
    {
        $this->eventHandlers[$event][] = $handler;

        return $this;
    }

    public function dispatch(string $event, array $payload = []): self
    {
        if (isset($this->eventHandlers[$event])) {
            foreach ($this->eventHandlers[$event] as $handler) {
                call_user_func($handler, $payload);
            }
        }

        return $this;
    }
}