Also, are there any particular resources that you would recommend for beginners? I'm looking forward to reading this article since it might expose the low-level details of how, say, message passing works under the hood. Most of the guides are a bit too "beginner-oriented"; I'd love to find something that pulls up the carpets to reveal all the infrastructure underneath.
If you are already familiar with high-level Objective-C, I would recommend looking at the headers for the language runtime. All of the inner workings are exposed as C functions you can play with. Also take a look at Mike Ash's blog, which dives into a lot of details: https://mikeash.com/pyblog/?tag=objectivec
Swift is the future Apple is pushing to developers. There is an insane amount of Objective C in the world for sure, so it's not going away completely, but I expect more new work will choose Swift, and eventually Objective C will be relegated to Apple devs working on OS X itself, plus legacy apps.
Also, are there any particular resources that you would recommend for beginners? I'm looking forward to reading this article since it might expose the low-level details of how, say, message passing works under the hood. Most of the guides are a bit too "beginner-oriented"; I'd love to find something that pulls up the carpets to reveal all the infrastructure underneath.