The problem is that Rust sees arrays as a fixed length array known at compile time. Simply put, you either have to use Vec<T> or wrap your own array implementation in unsafe code (which I would highly discourage). The Rust developers (as I gather) implemented Vec<T> so that they could handle all of the memory issues for developers. Some other users have expressed concerns for this approach. You can read the thread here and see a blog response by another user about unsafe code