Struct Watcher

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

An observer for a value.

The Watcher can get the current value, and will be notified when the value changes. Only the most recent value is accessible, and if the thread with the Watchable changes the value faster than the thread with the Watcher can keep up with, then it’ll miss in-between values. When the thread changing the Watchable pauses updating, the Watcher will always end up reporting the most recent state eventually.

Implementations

impl<T: Clone + Eq> Watcher<T>

pub fn get(&self) -> Result<T, Disconnected>

Returns the currently held value.

Returns Err(Disconnected) if the original Watchable was dropped.

pub fn updated(&mut self) -> WatchNextFut<'_, T>

Returns a future completing with Ok(value) once a new value is set, or with Err(Disconnected) if the connected Watchable was dropped.

Cancel Safety

The returned future is cancel-safe.

pub fn stream(self) -> WatcherStream<T>

Returns a stream which will yield the most recent values as items.

The first item of the stream is the current value, so that this stream can be easily used to operate on the most recent value.

Note however, that only the last item is stored. If the stream is not polled when an item is available it can be replaced with another item by the time it is polled.

This stream ends once the original Watchable has been dropped.

Cancel Safety

The returned stream is cancel-safe.

pub fn stream_updates_only(self) -> WatcherStream<T>

Returns a stream which will yield the most recent values as items, starting from the next unobserved future value.

This means this stream will only yield values when the watched value changes, the value stored at the time the stream is created is not yielded.

Note however, that only the last item is stored. If the stream is not polled when an item is available it can be replaced with another item by the time it is polled.

This stream ends once the original Watchable has been dropped.

Cancel Safety

The returned stream is cancel-safe.

impl<T: Clone + Eq> Watcher<Option<T>>

pub fn initialized(&mut self) -> WatchInitializedFut<'_, T>

Returns a future completing once the value is set to Some value.

If the current value is Some value, this future will resolve immediately.

This is a utility for the common case of storing an Option inside a Watchable.

Trait Implementations

impl<T: Clone> Clone for Watcher<T>

fn clone(&self) -> Watcher<T>

Returns a copy of the value.

fn clone_from(&mut self, source: &Self)

Performs copy-assignment from source.

impl<T: Debug> Debug for Watcher<T>

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

Formats the value using the given formatter.