Swift's proposal with copy on write is the sort of thing I was suggesting to make the borrow checker more ergonomic. It is going to be optional though, which I

Swift's proposal with copy on write is the sort of thing I was suggesting to make the borrow checker more ergonomic. It is going to be optional though, which I think takes some of the utility away. I want much stronger safety guarantees in the overall infrastructure than that would provide. Linear types in haskell would provide that, but speaking of some data structures being difficult, Haskell makes largely the same ones problematic. Ada has a borrow checker of sorts, but it makes unchecked_deallocate UB. As long as you don't free memory it doesn't have UB. That isn't a bad trade really, but it still isn't completely impossible to do bad things with access types and they aren't that ergonomic either. I don't know much about the others you mentioned. There is definitely a space for a friendlier enforcement of ownership that makes strong guarantees. But again, the borrow checker isn't my main pain point in rust, its the static strong typing with no duck typing for generics. It makes for nice error messages, but it makes other stuff hard.