Rust isn’t functional, so if you have state that’s shared in some way you can’t expect it to be immutable unless you manage it immutably. However you are assure

Rust isn’t functional, so if you have state that’s shared in some way you can’t expect it to be immutable unless you manage it immutably. However you are assured that you won’t need to worry about thread safety and reentrant code in rust because you are guaranteed the same memory won’t be modified or modified/read at the same time by two threads. Obviously in single threaded asynchronous code this doesn’t happen anyways. That said, if you don’t use shared state that allows multiple borrows, you won’t see state changing between futures even in the single threaded cases due to the ownership model of rust.