Struct async_once_cell::future::OnceCell

pub struct OnceCell<T> { /* fields omitted */ }

A thread-safe cell which can be written to only once.

This allows initialization using an async closure which is guaranteed to only be called once.

Implementations

impl<T> OnceCell<T>

pub const fn new() -> Self

Creates a new empty cell.

pub async fn get_or_init(&self, init: impl Future<Output = T>) -> &T

Gets the contents of the cell, initializing it with init if the cell was empty.

Many tasks may call get_or_init concurrently with different initializing futures, but it is guaranteed that only one future will be executed as long as the resuting future is polled to completion.

If f panics, the panic is propagated to the caller, and the cell remains uninitialized.

If the Future returned by this function is dropped prior to completion, the cell remains uninitialized (and another init futures may be selected for polling).

It is an error to reentrantly initialize the cell from init. The current implementation deadlocks, but will recover if the offending task is dropped.

pub async fn get_or_try_init<E>(
    &self,
    init: impl Future<Output = Result<T, E>>
) -> Result<&T, E>

Gets the contents of the cell, initializing it with init if the cell was empty. If the cell was empty and f failed, an error is returned.

If f panics, the panic is propagated to the caller, and the cell remains uninitialized.

If the Future returned by this function is dropped prior to completion, the cell remains uninitialized.

It is an error to reentrantly initialize the cell from init. The current implementation deadlocks, but will recover if the offending task is dropped.

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

Gets the reference to the underlying value.

Returns None if the cell is empty or being initialized. This method never blocks.

pub fn get_mut(&mut self) -> Option<&mut T>

Gets a mutable reference to the underlying value.

pub fn take(&mut self) -> Option<T>

Takes the value out of this OnceCell, moving it back to an uninitialized state.

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

Consumes the OnceCell, returning the wrapped value. Returns None if the cell was empty.

Trait Implementations

impl<T: Debug> Debug for OnceCell<T>

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

Formats the value using the given formatter.

impl<T: RefUnwindSafe + UnwindSafe> RefUnwindSafe for OnceCell<T>

impl<T: Send> Send for OnceCell<T>

impl<T: Sync + Send> Sync for OnceCell<T>

impl<T: UnwindSafe> UnwindSafe for OnceCell<T>