Code shared from the Rust Playground

playground.rs

use std::task::Poll;
use std::io::{Error, ErrorKind, Result};

fn err() -> Result<()> {
    Err(Error::new(ErrorKind::Other, "error"))
}

fn main() {
    println!("{:?}", test(Poll::Ready(err())));
    println!("{:?}", test2(err()));
    // println!("{:?}", test3(err()));
}

fn test(p: Poll<Result<()>>) -> Poll<Option<Result<()>>> {
    match p {
        Poll::Ready(v) => v,
        Poll::Pending => return Poll::Pending,
    }?;
    Poll::Ready(Some(Ok(())))
}

fn test2(r: Result<()>) -> Option<Result<()>> {
    match test(Poll::Ready(r)) {
        Poll::Ready(v) => v,
        _ => None,
    }
}

// fn test3(r: Result<()>) -> Option<Result<()>> {
//     r?;
//     Some(Ok(()))
// }