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Add future::delay #349

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Oct 29, 2019
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30 changes: 30 additions & 0 deletions src/future/future.rs
Original file line number Diff line number Diff line change
@@ -1,3 +1,11 @@
cfg_unstable! {
mod delay;

use std::time::Duration;

use delay::DelayFuture;
}

extension_trait! {
use std::pin::Pin;
use std::ops::{Deref, DerefMut};
Expand Down Expand Up @@ -99,6 +107,28 @@ extension_trait! {
}

pub trait FutureExt: std::future::Future {
/// Returns a Future that delays execution for a specified time.
///
/// # Examples
///
/// ```
/// # async_std::task::block_on(async {
/// use async_std::prelude::*;
/// use async_std::future;
/// use std::time::Duration;
///
/// let a = future::ready(1).delay(Duration::from_millis(2000));
/// dbg!(a.await);
/// # })
/// ```
#[cfg_attr(feature = "docs", doc(cfg(unstable)))]
#[cfg(any(feature = "unstable", feature = "docs"))]
fn delay(self, dur: Duration) -> impl Future<Output = Self::Output> [DelayFuture<Self>]
where
Self: Future + Sized
{
DelayFuture::new(self, dur)
}
}

impl<F: Future + Unpin + ?Sized> Future for Box<F> {
Expand Down
43 changes: 43 additions & 0 deletions src/future/future/delay.rs
Original file line number Diff line number Diff line change
@@ -0,0 +1,43 @@
use std::pin::Pin;
use std::time::Duration;

use futures_timer::Delay;
use pin_project_lite::pin_project;

use crate::future::Future;
use crate::task::{Context, Poll};

pin_project! {
#[doc(hidden)]
#[derive(Debug)]
pub struct DelayFuture<F> {
#[pin]
future: F,
#[pin]
delay: Delay,
}
}

impl<F> DelayFuture<F> {
pub fn new(future: F, dur: Duration) -> DelayFuture<F> {
let delay = Delay::new(dur);

DelayFuture { future, delay }
}
}

impl<F: Future> Future for DelayFuture<F> {
type Output = F::Output;

fn poll(self: Pin<&mut Self>, cx: &mut Context<'_>) -> Poll<Self::Output> {
let this = self.project();

match this.delay.poll(cx) {
Poll::Pending => Poll::Pending,
Poll::Ready(_) => match this.future.poll(cx) {
Poll::Ready(v) => Poll::Ready(v),
Poll::Pending => Poll::Pending,
},
}
}
}