The rust standard library does make targeted use of unchecked arithmetic when the containing type can ensure that that overflow never happens and benchmarks hav

The rust standard library does make targeted use of unchecked arithmetic when the containing type can ensure that that overflow never happens and benchmarks have shown that it benefits performance. E.g. in various iterator implementations. Which means the unsafe code has to be written and encapsulated once, users can now use safe for loops and still get that performance benefit.