Decoupling from a service locator - shouldn’t that be: don’t use a service locator?

Well, not really, since there are lots of valid use cases for using a service locator. The main use case is for making things lazy-loading (yes, you can also use some kind of proxy mechanism for that, but let’s assume you need something simpler). Say we have this EventDispatcher class:

class EventDispatcher
{
    public function __construct(array $listeners)
    {
        $this->listeners = $listeners;
    }

    public function dispatch($event)
    {
        foreach ($this->listeners[$event] as $listener) {
            $listener->notify();
        }
    }
}

Now it appears that some event listeners are rather expensive to instantiate. And, even though it may never be notified (because it listens to a rare event), in order to register any event listener, we need to instantiate it: