Protocol Oriented Programming (in Swift) – WWDC

You don't have to focus on the in Swift part with what the new protocol extensions. The first section is a good general discussion of the downsides of Object Oriented Programming (Class oriented really) and a simple illustration of an alternative approach. Watch the end too where it covers when OOP is appropriate.

The new Swift Protocol extensions are cool but aren't really the right place to start looking at Swift.

Am I only one afraid that magic of protocol extensions can end up with really hard to figure out behavior between types? As much as these concepts seems powerful to me, they also look like soon-to-be hell on earth for bigger teams working on same project.