tokio-stream 0.1.18

Utilities to work with `Stream` and `tokio`.
Documentation 
1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
35
36
37
38
39
40
41
42
43
44
45
46
47
48
49
50
51
52

use crate::{Iter, Stream};

use core::option;
use core::pin::Pin;
use core::task::{Context, Poll};

/// Stream for the [`once`](fn@once) function.
#[derive(Debug)]
#[must_use = "streams do nothing unless polled"]
pub struct Once<T> {
    iter: Iter<option::IntoIter<T>>,
}

impl<I> Unpin for Once<I> {}

/// Creates a stream that emits an element exactly once.
///
/// The returned stream is immediately ready and emits the provided value once.
///
/// # Examples
///
/// ```
/// use tokio_stream::{self as stream, StreamExt};
///
/// # #[tokio::main(flavor = "current_thread")]
/// # async fn main() {
/// // one is the loneliest number
/// let mut one = stream::once(1);
///
/// assert_eq!(Some(1), one.next().await);
///
/// // just one, that's all we get
/// assert_eq!(None, one.next().await);
/// # }
/// ```
pub fn once<T>(value: T) -> Once<T> {
    Once {
        iter: crate::iter(Some(value)),
    }
}

impl<T> Stream for Once<T> {
    type Item = T;

    fn poll_next(mut self: Pin<&mut Self>, cx: &mut Context<'_>) -> Poll<Option<T>> {
        Pin::new(&mut self.iter).poll_next(cx)
    }

    fn size_hint(&self) -> (usize, Option<usize>) {
        self.iter.size_hint()
    }
}