Swift Protocol Extensions as Mixins – And How Do You Test That?

I found a very useful distinction by Matthijs Hollemans to grasp what protocol extensions in Swift 2 can be: instead of interfaces, they are traits or even mixins. At the same time, I want to raise awareness for misuse: just because behavior is mixed-in doesn’t mean it’s additional behavior. The code may live in another file, but its functionality can still clutter your objects.

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