Struct WatchStream

pub struct WatchStream<T> { /* private fields */ }

A wrapper around tokio::sync::watch::Receiver that implements Stream.

This stream will start by yielding the current value when the WatchStream is polled, regardless of whether it was the initial value or sent afterwards, unless you use WatchStream<T>::from_changes.

Examples

use tokio_stream::{StreamExt, wrappers::WatchStream};
use tokio::sync::watch;

let (tx, rx) = watch::channel("hello");
let mut rx = WatchStream::new(rx);

assert_eq!(rx.next().await, Some("hello"));

tx.send("goodbye").unwrap();
assert_eq!(rx.next().await, Some("goodbye"));

use tokio_stream::{StreamExt, wrappers::WatchStream};
use tokio::sync::watch;

let (tx, rx) = watch::channel("hello");
let mut rx = WatchStream::new(rx);

// existing rx output with "hello" is ignored here

tx.send("goodbye").unwrap();
assert_eq!(rx.next().await, Some("goodbye"));

Example with WatchStream<T>::from_changes:

use futures::future::FutureExt;
use tokio::sync::watch;
use tokio_stream::{StreamExt, wrappers::WatchStream};

let (tx, rx) = watch::channel("hello");
let mut rx = WatchStream::from_changes(rx);

// no output from rx is available at this point - let's check this:
assert!(rx.next().now_or_never().is_none());

tx.send("goodbye").unwrap();
assert_eq!(rx.next().await, Some("goodbye"));

Implementations

impl<T: 'static + Clone + Send + Sync> WatchStream<T>

pub fn new(rx: Receiver<T>) -> Self

Create a new WatchStream.

pub fn from_changes(rx: Receiver<T>) -> Self

Create a new WatchStream that waits for the value to be changed.

Trait Implementations

impl<T> Debug for WatchStream<T>

fn fmt(&self, f: &mut Formatter<'_>) -> Result

Formats the value using the given formatter.

impl<T: 'static + Clone + Send + Sync> From<Receiver<T>> for WatchStream<T>

fn from(recv: Receiver<T>) -> Self

Converts to this type from the input type.

impl<T: Clone + 'static + Send + Sync> Stream for WatchStream<T>

type Item = T

Values yielded by the stream.

fn poll_next( self: Pin<&mut Self>, cx: &mut Context<'_>, ) -> Poll<Option<Self::Item>>

Attempt to pull out the next value of this stream, registering the current task for wakeup if the value is not yet available, and returning None if the stream is exhausted.

fn size_hint(&self) -> (usize, Option<usize>)

Returns the bounds on the remaining length of the stream.

impl<T> Unpin for WatchStream<T>