swift subclasses used in generics don't get called when inheriting from NSObject

Question

Partial Solution Update at the end!

Attached is code that produces odd behavior. I copied it out of a swift playground so it should run in one fine.

Answer 1

This is a second way to avoid the problem.

@matt originally suggested this but then deleted his answer. It is a good way to avoid the problem. His answer was simple. Mark the protocol with objc like this:

// The Protocol
@objc protocol P {
    init ()
    func doWork() -> String
}

This solves the above sample code and you now get the expected results. But doing this has side effects for swift. At least one of those is here:

How to use @objc protocol with optional and extensions at the same time?

For me, it began a chain of having to make all my protocols objc compatible. That made the change not worth it for my code base. I was also using extensions.

I decided to stay with my original answer at least until Apple fixes this bug or there is a less invasive solution.

I thought this one should be documented in case it helps someone else facing this problem.