I've actually used this system as a student in a programming language design class, in which we had to implement semispace and mark-and-sweep collectors. I had the misfortune (unique in 2 sections of the class that semester) of running into a bug in the framework, but I believe that got fixed, and it was otherwise pretty dang cool.
We used C++ to write a game and _SOMEHOW_ without knowing properly about how GC worked - learned to write our own garbage collectors for projectiles that went out of screen and enemies that died.
:) It was basically the eye opener for how GC's worked. Though I am sure it's faaaaaar more complicated than the Sets we used to keep track. It still made me better at manually handling memory.
That being said, I prefer GC and/or Automatic Reference Counting at compile time. Still though, it was a nice "feeling" to manage your own memory in an (incredibly small) project.
He's probably talking about ARC for Objective-C, that automatically releases references and allocations when it's impossible for those allocations to be used again in scope.
