I'm familiar with this issue. But it's a self-imposed problem, not a fundamental limitation relative to C++: the "same people" decided (at different points in time, to be fair) to make the `Future` trait use `&mut Self`, and to let specific futures hold self references.

This is a very different issue than the actual ability to express shared mutability in the language. With enough foresight, Rust could have "simply" used `&Self` and `UnsafeCell` for futures (and the current compiler hack with `!Unpin` is basically just replacing `&mut Self` with `&UnsafeCell<Self>` under the hood).