Wrong, wrong, wrong. As I said, race conditions caused by non-exclusive mutable access (such as modifying a collection while iterating over it) are trivially prevented by forbidding non-exclusive mutable access! Which is what Rust does. Not all race conditions can be prevented, obviously. But that does not mean that none of them can. I'm not sure what you mean by "local, syntax-based analysis" given that type systems are neither local nor syntax-based. Do you perhaps have a failure of imagination of what sorts of invariants a powerful type system is able to enforce?