@davy thank you for nice post about HRTB. I didn't know about it before. To be honest, I'm also having trouble to understand `Fn`, `FnOnce`, and `FnMut`, so I prefer to use custom traits like `MyFn` to understand what's going on: https://github.com/sergey-shandar/public/blob/main/hrtb/src/main.rs#L32