The problem is you either need the equivalent of the Rust borrow-checker to validate that the partition boundaries are respected or the partitions are just hint

The problem is you either need the equivalent of the Rust borrow-checker to validate that the partition boundaries are respected or the partitions are just hints which makes the scope of optimizations much smaller. It isn't GC but NeXTSTEP had allocation regions under this theory; that's where alloc:withZone: came from. In reality programmers mixed up the zones and there were way too many crashes as a result. Without some way to enforce the separation you just don't get much benefit.