Struct Watchable 

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

A wrapper around a value that notifies Watchers when the value is modified.

Only the most recent value is available to any observer, but the observer is guaranteed to be notified of the most recent value.

Implementations

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

pub fn new(value: T) -> Self

Creates a Watchable initialized to given value.

pub fn set(&self, value: T) -> Result<T, T>

Sets a new value.

Returns Ok(previous_value) if the value was different from the one set, or returns the provided value back as Err(value) if the value didn’t change.

Watchers are only notified if the value changed.

pub fn modify<F, R>(&self, f: F) -> R

where F: FnOnce(&mut T) -> R,

Atomically modifies the value using a closure.

The closure receives a mutable reference to the current value and may modify it in place. The read-modify-write is performed under a write lock, so it happens atomically with respect to other callers of Watchable::set, Watchable::modify, Watchable::get, and Watchers. The closure should therefore be fast and must not call back into this Watchable (doing so will deadlock).

Watchers are only notified if the value actually changed, as determined by Eq. Whatever the closure returns is forwarded as the return value of this method, which makes it convenient for expressing compare-and-swap:

let watchable = Watchable::new(42);

let swapped = watchable.modify(|value| {
    if *value == 42 {
        *value = 100;
        true
    } else {
        false
    }
});
assert!(swapped);
assert_eq!(watchable.get(), 100);

pub fn watch(&self) -> Direct<T>

Creates a Direct Watcher, allowing the value to be observed, but not modified.

pub fn get(&self) -> T

Returns the currently stored value.

pub fn has_watchers(&self) -> bool

Returns true when there are any watchers actively listening on changes, or false when all watchers have been dropped or none have been created yet.

Trait Implementations

impl<T> Clone for Watchable<T>

fn clone(&self) -> Self

Returns a duplicate of the value.

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

Performs copy-assignment from source.

impl<T: Debug> Debug for Watchable<T>

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

Formats the value using the given formatter.

impl<T: Default> Default for Watchable<T>

fn default() -> Watchable<T>

Returns the “default value” for a type.