alt Hacker Newssplit_at_mut is just unsafe code (and sibling comment mentioned it hours before you did). The borrow checker doesn't natively understand that.
split_at_mut is just unsafe code (and sibling comment mentioned it hours before you did). The borrow checker doesn't natively understand that.
It is safe btw. The difference is that it returns two mutable references vs. one shared ref and one mutable ref. But as they noted, a mutable ref can always be “downgraded” into a shared ref.