Struct SetOnce 

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

A cell that is set once, and that readers can wait on until it is.

It is a OnceCell that nobody initializes asynchronously, paired with an Event that wait sleeps on: set publishes the value with one compare-and-swap, and then sets the event, which wakes every waiter.

use nuclei::sync::SetOnce;

static GREETING: SetOnce<&str> = SetOnce::const_new();
assert!(GREETING.get().is_none());
assert!(GREETING.set("hello").is_ok());
assert_eq!(GREETING.get(), Some(&"hello"));
assert!(GREETING.set("again").is_err());

Implementations

impl<T> SetOnce<T>

pub const fn new() -> Self

An unset cell.

pub const fn const_new() -> Self

An unset cell, usable in a static.

pub fn new_with(value: Option<T>) -> Self

A cell that holds value if there is one, and is unset otherwise.

pub const fn const_new_with(value: T) -> Self

A cell that is set to value already, usable in a static.

pub fn initialized(&self) -> bool

Whether the cell holds a value.

pub fn get(&self) -> Option<&T>

The value, once set.

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

Sets the value, and wakes every task waiting in wait. One compare-and-swap publishes; never waits.

Errors

SetOnceError with the value when the cell is set already, or another call is setting it at this moment.

pub fn into_inner(self) -> Option<T>

Consumes the cell and returns its value, if it has one.

pub async fn wait(&self) -> &T

Waits until the cell is set, and returns the value: at once if it is set already.

Dropping the future withdraws the wait.

Trait Implementations

impl<T: Clone> Clone for SetOnce<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 SetOnce<T>

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

Formats the value using the given formatter.

impl<T> Default for SetOnce<T>

fn default() -> Self

Returns the “default value” for a type.

impl<T: Eq> Eq for SetOnce<T>

impl<T> From<T> for SetOnce<T>

fn from(value: T) -> Self

Converts to this type from the input type.

impl<T: PartialEq> PartialEq for SetOnce<T>

fn eq(&self, other: &Self) -> bool

Equality operator ==.

fn ne(&self, other: &Rhs) -> bool

Inequality operator !=.