1 | use super::assert_future; |
2 | use core::marker; |
3 | use core::pin::Pin; |
4 | use futures_core::future::{FusedFuture, Future}; |
5 | use futures_core::task::{Context, Poll}; |
6 | |
7 | /// Future for the [`pending()`] function. |
8 | #[derive (Debug)] |
9 | #[must_use = "futures do nothing unless you `.await` or poll them" ] |
10 | pub struct Pending<T> { |
11 | _data: marker::PhantomData<T>, |
12 | } |
13 | |
14 | impl<T> FusedFuture for Pending<T> { |
15 | fn is_terminated(&self) -> bool { |
16 | true |
17 | } |
18 | } |
19 | |
20 | /// Creates a future which never resolves, representing a computation that never |
21 | /// finishes. |
22 | /// |
23 | /// The returned future will forever return [`Poll::Pending`]. |
24 | /// |
25 | /// # Examples |
26 | /// |
27 | /// ```ignore |
28 | /// # futures::executor::block_on(async { |
29 | /// use futures::future; |
30 | /// |
31 | /// let future = future::pending(); |
32 | /// let () = future.await; |
33 | /// unreachable!(); |
34 | /// # }); |
35 | /// ``` |
36 | #[cfg_attr (docsrs, doc(alias = "never" ))] |
37 | pub fn pending<T>() -> Pending<T> { |
38 | assert_future::<T, _>(Pending { _data: marker::PhantomData }) |
39 | } |
40 | |
41 | impl<T> Future for Pending<T> { |
42 | type Output = T; |
43 | |
44 | fn poll(self: Pin<&mut Self>, _: &mut Context<'_>) -> Poll<T> { |
45 | Poll::Pending |
46 | } |
47 | } |
48 | |
49 | impl<T> Unpin for Pending<T> {} |
50 | |
51 | impl<T> Clone for Pending<T> { |
52 | fn clone(&self) -> Self { |
53 | pending() |
54 | } |
55 | } |
56 | |