And the problem with async in Rust is that it's really hard to prove a single owner across the await gap. In the other languages where I used async, Javascript

And the problem with async in Rust is that it's really hard to prove a single owner across the await gap. In the other languages where I used async, Javascript and C#, there is no penalty for using a variable across the async gap. The async keyword just means that something will block. (And plenty of other details, like your UI can paint itself.)