[gpm]

> or allow aliasing &mut in single-threaded circumstances where it's known to be safe (i.e. when the data is something primitive like an int, where it doesn't actually matter if it's overwritten while referenced).

Incidentally this is basically what the `Cell` type does. I suspect that making it the default wouldn't make it harder for me to reason about the code I'm working on - but it is an interesting proposal.