iterators had a lot of work done on them for this reason. although it doesn't always work. eg, once the difference between using a sign and unsigned value in a

iterators had a lot of work done on them for this reason. although it doesn't always work. eg, once the difference between using a sign and unsigned value in a loop was causing tustc to not be able to optimize out the checks and resulted in terrible performance for that loop, but it was non-trivial to figure this out