Getting the queue back out of an AnyScheduler?

[JetForMe]

I was trying to use this for testing, as shown in your examples, but my coded uses the queue both for .receive(on:) and for DispatchQueue.async calls (when it calls the delegate we also employ). I can, of course, simply keep the queue reference around and only make the AnyScheduler in the .receive(on:) calls, but if there's a way to recover the DQ, that would be handy.

[mbrandonw]

Hey @JetForMe, this is a good question!

Unfortunately it is not safe to expose a dispatch queue inside the AnyScheduler because it's not necessarily always powered by a real life dispatch queue. You can have a AnySchedulerOf<DispatchQueue> that secretly is a test scheduler or immediate scheduler under the hood, and so there is not real dispatch queue to expose.

The best we could do is expose a var base: Any that exposes the underlying scheduler, but it would have to be Any because the type of the underlying scheduler has been completely forgotten about... which is the point of the AnyScheduler. But, if you try casting that Any to a DispatchQueue it will fail in tests because most likely you are using a test/immediate scheduler.

Having said that, you can still accomplish what you want without getting access to the underlying scheduler. The Scheduler protocol has a method called .schedule, and DispatchQueue's implementation simply calls .async { }. So you can just do:

scheduler.schedule { 
  // do work
}

Best of all, this works for all schedulers, whether you are really using a dispatch queue, test scheduler, immediate scheduler, etc.

[JetForMe]

Oh that's great, that's what I need.