It is compatible under Rust’s model (I’ve used it to implement safe io_uring interfaces specifically). ‘&mut Vec<u8>’ doesn’t just let you mutate contents or extend the allocation - you can call ‘mem::replace(…)’ and swap the allocation entirely. It’s morally equivalent to passing back and forth, and almost identical in the generated machine code (structure return values look a lot like mutable structure arguments at the register calling convention level). However it’s much less annoying to work with in practice - passing buffers back and forth and then reassigning them to the same variable name results in a lot of semantically irrelevant code to please the ownership model.