Function dispatch 

pub async fn dispatch<C, F, Fut>(
    args: &[impl AsRef<str>],
    handler: F,
) -> ExecutionResult
where
    C: SubCommands,
    F: FnOnce(C) -> Fut,
    Fut: Future<Output = Result<String, Error>>,

Parses arguments into C and executes handler on the parsed subcommand, returning an ExecutionResult.