[mikro]

Maybe it was a question about Grand Central Dispatch? https://developer.apple.com/documentation/DISPATCH

I also feel the same way about getting all but one question. I usually make it all the way to the end of a really grueling process before getting rejected.

[cableshaft]

Good guess, but I think I found what it actually was: Toll-Free Bridging[1]. Basically how you can use many Core Foundation types and NeXTSTEP classes interchangeably, like CFLocaleRef and NSLocale.

Never really had to use it myself, at least IIRC, but I was aware of the concept generally. But because I didn't answer by saying 'Toll-Free Bridging', I was done.

[1]: https://developer.apple.com/library/archive/documentation/Ge...