This is a really great blog post by Matthijs Hollemans (author of the iOS Apprentice book I just finished reading) about the power of implementing protocol extensions/mixins/traits in your code to help reduce code-reuse, and make it more flexible.

It is a different way of thinking, but in my opinion, a much better way to code. I’m excited to implement protocol extensions into my app!

http://matthijshollemans.com/2015/07/22/mixins-and-traits-in-swift-2/