mini-redis/Tutorial/Future.rs

#![allow(non_snake_case)]

use futures::future::poll_fn;
use std::future::Future;
use std::pin::Pin;
use std::task::{Context, Poll};
use std::time::{Duration, Instant};

struct Delay {
    when: Instant,
}

impl Future for Delay {
    type Output = &'static str;

    fn poll(self: Pin<&mut Self>, cx: &mut Context<'_>) -> Poll<&'static str> {
        if Instant::now() >= self.when {
            println!("Hello world");
            Poll::Ready("done")
        } else {
            // Ignore this line for now.
            cx.waker().wake_by_ref();
            Poll::Pending
        }
    }
}

#[tokio::main]
async fn main() {
    let when = Instant::now() + Duration::from_millis(10);
    let mut delay = Some(Delay { when });

    poll_fn(move |cx| {
        let mut delay = delay.take().unwrap();
        let res = Pin::new(&mut delay).poll(cx);
        assert!(res.is_pending());
        tokio::spawn(async move {
            delay.await;
        });

        Poll::Ready(())
    })
    .await;

    /*
    let when = Instant::now() + Duration::from_millis(1000);
    let future = Delay { when };

    let out = future.await;
    assert_eq!(out, "done");

    let when = Instant::now() + Duration::from_millis(10);
    let mut delay = Some(Delay { when });
    */
}