tokio_stream/
empty.rs

1use crate::Stream;
2
3use core::marker::PhantomData;
4use core::pin::Pin;
5use core::task::{Context, Poll};
6
7/// Stream for the [`empty`](fn@empty) function.
8#[derive(Debug)]
9#[must_use = "streams do nothing unless polled"]
10pub struct Empty<T>(PhantomData<T>);
11
12impl<T> Unpin for Empty<T> {}
13unsafe impl<T> Send for Empty<T> {}
14unsafe impl<T> Sync for Empty<T> {}
15
16/// Creates a stream that yields nothing.
17///
18/// The returned stream is immediately ready and returns `None`. Use
19/// [`stream::pending()`](super::pending()) to obtain a stream that is never
20/// ready.
21///
22/// # Examples
23///
24/// Basic usage:
25///
26/// ```
27/// use tokio_stream::{self as stream, StreamExt};
28///
29/// # #[tokio::main(flavor = "current_thread")]
30/// # async fn main() {
31/// let mut none = stream::empty::<i32>();
32///
33/// assert_eq!(None, none.next().await);
34/// # }
35/// ```
36pub const fn empty<T>() -> Empty<T> {
37    Empty(PhantomData)
38}
39
40impl<T> Stream for Empty<T> {
41    type Item = T;
42
43    fn poll_next(self: Pin<&mut Self>, _cx: &mut Context<'_>) -> Poll<Option<T>> {
44        #[cfg(feature = "rt")]
45        {
46            use tokio::task::coop;
47
48            let coop = std::task::ready!(coop::poll_proceed(_cx));
49            coop.made_progress();
50        }
51
52        Poll::Ready(None)
53    }
54
55    fn size_hint(&self) -> (usize, Option<usize>) {
56        (0, Some(0))
57    }
58}
tokio_stream/empty.rs

tokio_stream/
empty.rs
