Function forward 

pub async fn forward<S: Clone + PartialEq, T>(
    progress: Receiver<Option<Progress<S>>>,
    work: impl Future<Output = T>,
    report: impl Fn(Progress<S>),
) -> T

Run work to its end, calling report on this task with the progress it reports into progress. A host that redraws more slowly than work reports sees the newest value, never an older one after it; a report made just before work ends is still delivered, and none twice. What the watch held before progress subscribed belongs to an earlier operation and is never delivered.