So, last year when all the excitement was frothing about this Protocol-Oriented Programming “revolution,” First Protocol-Oriented Language and all — did you take a quick look and chuckle to yourself , thinking “Ah, they’ve rediscovered Mixin-Based Programming, isn’t that cute?” and move on? Yeah, us too. But it turns out there is a good bit more depth to plumb! Here’s an excellent tutorial style introduction, released as a teaser for the RWDevCon 2016 Vault video collection:

RWDevCon 2016 Session 303: Introduction to Protocol-Oriented Programming

Here are the key points:

• protocols with extensions are almost perfectly superior to inheritance
  • you can do almost everything you can with inheritance
  • and, they can work with value types
  • and, they allow retroactive modeling
• but, protocols with associated types (PATs) are different beasts
  • you give up dynamic dispatch
  • but you can model more intricate type relations

Or if you just want one nugget to mull over, I’d say most of it is in this slide:

And here is an absolutely essential series on associated types from Russ Bishop:

Swift Associated Types

Sometimes I think type theory is deliberately obtuse and all those functional programming hipster kids are just bull-shitting as if they understood one word of it…

Swift Associated Types, cont.

I don’t feel like I fully covered one aspect of protocols with associated types: why can they be such a pain to work with?

Swift: Why Associated Types?

So the philosophical answer to the question of Why Associated Types? is that the Swift core team believes they are a better way to model concepts. They don’t have the problem of multiple conformances, they encapsulate the details of a concept cleanly, and they’re less fragile.

And there you have it. By way of example, here’s a few practical applications of protocols to make common tasks more elegant:

Protocol-Oriented MVVM in Swift 2.0

Protocol Extensions, Meet List Controllers

Stupid Swift Tricks #5: Pickable Enums

Upgrade your TableViews with Loading State

And a wide-ranging selection of other inside baseball style musings on generics and protocols to help you grok the gestalt here:

Swift Protocol Extension Weirdness

Improved Protocol-Oriented Programming with Untyped Type Aliases (part 1) and part 2

Generic Protocols & Their Shortcomings

Trimming Swift generics

Generics and the Art of Inference Part 1 of 3

What the 55 Swift Standard Library Protocols Taught Me

Protocols with Associated Types, and How They Got That Way

Protocol-Oriented Problems and the Immutable ‘self’ Error

The why of nonmutating

Beyond Crusty: Real-World Protocols

Working with Swift: Adopt a Protocol or Pass a Function?

Doubling Down on Protocol-Oriented Programming

Plenty there to keep you pondering for a while we trust!

UPDATES:

Practical Protocol-Oriented-Programming slides from Natasha The Robot