Marc Morera has posted an interesting article to his site suggesting a re-thinking of how event listeners are used in applications and libraries.

Let’s talk about Event Listeners. Do you know what an Event Listener is? Well, if you are used to working with Symfony, then you should know what is intended for. If you don’t, don’t hesitate to take a look at the Symfony documentation. This post aims to start a small discussion about how an Event Listener should look like if we really want to keep things decoupled.

The starts with a brief summary of the post (tl;dr) for those in a hurry but goes on to explain things in a bit more detail too. He starts by laying a foundation, introducing what event listeners are. He also shows how they're commonly implemented and used (in Symfony2 specifically but it applies more generally too) to trigger actions in applications. He suggests decoupling things a bit more from the flow of the action and allowing, in this case, access to both the order and the customer (on a "order created" action). He takes it one step further and decouples the sending of an email into a service and then creates an instance of this when needed in the event and not before.