> Naive ARC is AFAIK very expensive as it causes a lot of updates at each pointer... Yes, and I think that's why people shy away from it. Language design can h

> Naive ARC is AFAIK very expensive as it causes a lot of updates at each pointer... Yes, and I think that's why people shy away from it. Language design can help a lot though: Array languages use reference counting almost exclusively because nesting objects is uncommon. That means no pointers to chase the vast majority of the time. > if ARC is what you think it is, how is it not an implementation of GC? Garbage Collection involves crawling live objects from roots to determine what's still alive. If you're not doing that, you might still be doing automatic memory management, but you're not doing GC. There's tricks (gardens, barriers, treadmills, colouring, etc) to do less work or less work at a time, but it remains predicated on the assumption is that you have more garbage than you have live objects so you're doing less work by only crawling the live objects. If this is true, then GC should be a win, but it's not true an awful lot of the time, which is why manual memory management always beats GC for performance (latency and throughput). [†]: notwithstanding your earlier point about pointer chasing... > I'll check out linear lisp if I can find the time. I can recommend everything Baker has written on this subject: it's all gold.