This is in case you turn the Vec into a raw pointer (using as_ptr() and mem::forget) so that you can pass ownership over FFI or something. In this case it is no

This is in case you turn the Vec into a raw pointer (using as_ptr() and mem::forget) so that you can pass ownership over FFI or something. In this case it is not recommended that you free it by calling free(), it is recommended that you free it by using from_raw_parts to reconstruct a new vector and let it drop. You need the second vec because the first vec is gone at this point. If it wasn't gone you could just let the destructor run. In Rust Vec and Box also work as the malloc primitives; if you absolutely need to allocate contiguous memory of runtime-known size the best way to do it is to allocate a Vec and then extract the pointer from it. (There is a proper allocation API coming soon; and of course you can just call malloc/free, but this is the recommended way of doing it)