Toll-free bridging between a runtime that uses a tracing GC and one that doesn't share that exact same tracing GC is impossible. It's just a desperate stop gap.

Toll-free bridging between a runtime that uses a tracing GC and one that doesn't share that exact same tracing GC is impossible. It's just a desperate stop gap. And another thing! I assume this is referring to Java and Obj-C. There's an alternate-universe proposal where this could have worked: Apple did actually briefly flirt with adding a traditional GC to Obj-C. If that had been successful, they could have essentially imported the Java memory model into Obj-C. However, the GC wasn't popular and was supplanted by Automatic Reference Counting. I'm not sure if that's what anyone actually had in mind (I can't recall when the Java bridge and Obj-C GC started and stopped) but I think it would have been technically feasible. I'd guess the iPhone would be very different in that world, or at least delayed, because GC has higher memory requirements and collector pauses make it hard to maintain a smooth UI. But you can make something like an iPhone using mostly Java, as Google proved with Android (eventually!)