Johan Andrén

Let's get some consensus on the operator to start with, before we dig into a nice operator factory shortcut. I'm somewhat thawing to the idea with a built in `Either`...

Congrats @longshorej ! Let's close it for now and re-open/revisit in the future.

Indeed, would you mind PR:ing a fix?

I'd expect the intended logic would be to complete if the exception is a `akka.stream.SubscriptionWithCancelException.NonFailureCancellation` and fail for other exeptions

Thanks, we missed that.

Probably hard to abstract over since the fanout output-arity is represented by concrete FanoutShape classes. Alternative is to provide only one "combiner" for arity two but then the usefulness is...

To follow convention in other factories it should be `combineMat(Sink[U, M1], Sink[U, M2])((M1, M2) => M3): Sink[U, M3]`. I think it is a good idea.

Hmm, looking at the existing `combine` it's a 2-mandatory-sinks plus varargs, you think it would be possible to pull off matching that? If we limit the type of the matval...

Starting to think that this was the reason there never was a `Sink.combineMat` to start with :) If you want to broadcast to 6 downstream, I don't think you want...

Ok, what about doing the original combineMat idea with 2-arity for now, and maybe mention in the scala docs that for higher arities, use GraphDSL?