On top of the cost of the extra pointer lookup, you also run into cache coherency issues when dealing with threading. So then you need to use atomic ops or lock

On top of the cost of the extra pointer lookup, you also run into cache coherency issues when dealing with threading. So then you need to use atomic ops or locks or cache flushing which makes it even more expensive. Rust is better suited to deal with it since there's a similar issue with refcounting across threads, so you might be able to get away with doing it for objects that are exclusive to one thread.