[pcwalton]

> This should be obvious because pure reference counting requires modifying counts whenever locals are assigned, which happen orders of magnitude more often than main memory updates, and now each local assignment requires touching main memory too.

I guess so, but it's worth noting that this isn't the case in Rust, because Rc benefits from move semantics. Most assignments don't touch the reference counts at all.

[naasking]

Right, Rust's borrowing is like the optimization link I provided, just slightly less general IIRC.