async_std/stream/
pending.rs

1use core::marker::PhantomData;
2use core::pin::Pin;
3use core::task::{Context, Poll};
4
5use crate::stream::{DoubleEndedStream, ExactSizeStream, FusedStream, Stream};
6
7/// A stream that never returns any items.
8///
9/// This stream is created by the [`pending`] function. See its
10/// documentation for more.
11///
12/// [`pending`]: fn.pending.html
13#[derive(Debug)]
14pub struct Pending<T> {
15    _marker: PhantomData<T>,
16}
17
18/// Creates a stream that never returns any items.
19///
20/// The returned stream will always return `Pending` when polled.
21/// # Examples
22///
23/// ```
24/// # async_std::task::block_on(async {
25/// #
26/// use std::time::Duration;
27///
28/// use async_std::prelude::*;
29/// use async_std::stream;
30///
31/// let dur = Duration::from_millis(100);
32/// let mut s = stream::pending::<()>().timeout(dur);
33///
34/// let item = s.next().await;
35///
36/// assert!(item.is_some());
37/// assert!(item.unwrap().is_err());
38///
39/// #
40/// # })
41/// ```
42pub fn pending<T>() -> Pending<T> {
43    Pending {
44        _marker: PhantomData,
45    }
46}
47
48impl<T> Stream for Pending<T> {
49    type Item = T;
50
51    fn poll_next(self: Pin<&mut Self>, _: &mut Context<'_>) -> Poll<Option<T>> {
52        Poll::Pending
53    }
54}
55
56impl<T> DoubleEndedStream for Pending<T> {
57    fn poll_next_back(self: Pin<&mut Self>, _: &mut Context<'_>) -> Poll<Option<T>> {
58        Poll::Pending
59    }
60}
61
62impl<T> FusedStream for Pending<T> {}
63
64impl<T> ExactSizeStream for Pending<T> {
65    fn len(&self) -> usize {
66        0
67    }
68}
async_std/stream/pending.rs

async_std/stream/
pending.rs
