EventDispatch implements the Mediator pattern, not the Observer pattern

[johnkary]

Anthony Ferrara @ircmaxell does a great job of pointing out the differences between the Mediator and Observer pattern in his blog post Handling Plugins In PHP.

The two patterns appear very similar but differ in which object does the event emitting:

An implementation of the Observer pattern would allow each object/entity/service to individually allow subscribing to its events and it would notify all listeners itself: OrderPersister->notify('order.create', $order)

But a Mediator pattern implementation would be like the Symfony EventDispatcher object that is centrally-configured with listeners and then notifies those listeners of events on behalf of its external collaborators: Inside a controller $this->persister->create($order); then inside Persister::create() -- $this->dispatcher->notify('order.create', $order)

🌊

[wouterj]

This should be merged in 2.2, 2.0 and 2.1 are deprecated

[johnkary]

@wouterj Should I open a new PR against 2.2?

[wouterj]

No, we'll cherrypick the commit when merging. It's just a tip for the next time.

[weaverryan]

Hey John!

Ah, thanks for the fix! In fact, we just had a talk at the Nashville PHP meetup about 2 weeks ago where this was also explained, and had the same thought there (though not with as much clarity as you explained). I've patched this into the 2.2 branch at sha: 5c0e52c

Thanks!