That's not entirely true, it would be similar to `Arc<T>` everywhere, because the Swift compiler and the language are by default not concurrency safe (there're

That's not entirely true, it would be similar to `Arc<T>` everywhere, because the Swift compiler and the language are by default not concurrency safe (there're runtime features to detect issues here, similar to RefCell though). This means that Rust has to use `Arc<Mutex<T>>` in order to satisfy the compiler, Swift gets away with `Arc<T>` (and I'm currently not sure, but it might even be only `Rc<T>`) because the compiler doesn't prevent it.