It is "const enough", as in, there is nothing preventing it from being called at compile time, in fact with nightly features (and no changes to the async fn), y

It is "const enough", as in, there is nothing preventing it from being called at compile time, in fact with nightly features (and no changes to the async fn), you can call it at compile time just fine. I also put const fn there to emphasize that it really can't do all that much beside constructing the state machine.