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tokio-stream: WatchStream: yield the current value #3576

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Mar 5, 2021
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37 changes: 36 additions & 1 deletion tokio-stream/src/wrappers/watch.rs
Original file line number Diff line number Diff line change
Expand Up @@ -10,6 +10,41 @@ use tokio::sync::watch::error::RecvError;

/// A wrapper around [`tokio::sync::watch::Receiver`] that implements [`Stream`].
///
/// This stream will always start by yielding the current value when the WatchStream is polled,
/// regardles of whether it was the initial value or sent afterwards.
///
/// # Examples
///
/// ```
/// # #[tokio::main]
/// # async fn main() {
/// 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"));
/// # }
/// ```
///
/// ```
/// # #[tokio::main]
/// # async fn main() {
/// use tokio_stream::{StreamExt, wrappers::WatchStream};
/// use tokio::sync::watch;
///
/// let (tx, rx) = watch::channel("hello");
/// let mut rx = WatchStream::new(rx);
///
/// tx.send("goodbye").unwrap();
/// assert_eq!(rx.next().await, Some("goodbye"));
/// # }
/// ```
///
/// [`tokio::sync::watch::Receiver`]: struct@tokio::sync::watch::Receiver
/// [`Stream`]: trait@crate::Stream
#[cfg_attr(docsrs, doc(cfg(feature = "sync")))]
Expand All @@ -28,7 +63,7 @@ impl<T: 'static + Clone + Unpin + Send + Sync> WatchStream<T> {
/// Create a new `WatchStream`.
pub fn new(rx: Receiver<T>) -> Self {
Self {
inner: ReusableBoxFuture::new(make_future(rx)),
inner: ReusableBoxFuture::new(async move { (Ok(()), rx) }),
}
}
}
Expand Down