[][src]Struct std::lazy::SyncOnceCell

pub struct SyncOnceCell<T> { /* fields omitted */ }
🔬 This is a nightly-only experimental API. (once_cell #74465)

A synchronization primitive which can be written to only once.

This type is a thread-safe OnceCell.

Examples

#![feature(once_cell)]

use std::lazy::SyncOnceCell;

static CELL: SyncOnceCell<String> = SyncOnceCell::new();
assert!(CELL.get().is_none());

std::thread::spawn(|| {
    let value: &String = CELL.get_or_init(|| {
        "Hello, World!".to_string()
    });
    assert_eq!(value, "Hello, World!");
}).join().unwrap();

let value: Option<&String> = CELL.get();
assert!(value.is_some());
assert_eq!(value.unwrap().as_str(), "Hello, World!");
Run

Implementations

impl<T> SyncOnceCell<T>[src]

pub const fn new() -> SyncOnceCell<T>[src]

🔬 This is a nightly-only experimental API. (once_cell #74465)

Creates a new empty cell.

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

🔬 This is a nightly-only experimental API. (once_cell #74465)

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>[src]

🔬 This is a nightly-only experimental API. (once_cell #74465)

Gets the mutable reference to the underlying value.

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

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

🔬 This is a nightly-only experimental API. (once_cell #74465)

Sets the contents of this cell to value.

Returns Ok(()) if the cell's value was updated.

Examples

#![feature(once_cell)]

use std::lazy::SyncOnceCell;

static CELL: SyncOnceCell<i32> = SyncOnceCell::new();

fn main() {
    assert!(CELL.get().is_none());

    std::thread::spawn(|| {
        assert_eq!(CELL.set(92), Ok(()));
    }).join().unwrap();

    assert_eq!(CELL.set(62), Err(62));
    assert_eq!(CELL.get(), Some(&92));
}
Run

pub fn get_or_init<F>(&self, f: F) -> &T

Notable traits for &'_ mut F

impl<'_, F> Future for &'_ mut F where
    F: Unpin + Future + ?Sized
type Output = <F as Future>::Output;impl<'_, I> Iterator for &'_ mut I where
    I: Iterator + ?Sized
type Item = <I as Iterator>::Item;impl<R: Read + ?Sized, '_> Read for &'_ mut Rimpl<W: Write + ?Sized, '_> Write for &'_ mut W
where
    F: FnOnce() -> T, 
[src]

🔬 This is a nightly-only experimental API. (once_cell #74465)

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

Many threads may call get_or_init concurrently with different initializing functions, but it is guaranteed that only one function will be executed.

Panics

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

It is an error to reentrantly initialize the cell from f. The exact outcome is unspecified. Current implementation deadlocks, but this may be changed to a panic in the future.

Examples

#![feature(once_cell)]

use std::lazy::SyncOnceCell;

let cell = SyncOnceCell::new();
let value = cell.get_or_init(|| 92);
assert_eq!(value, &92);
let value = cell.get_or_init(|| unreachable!());
assert_eq!(value, &92);
Run

pub fn get_or_try_init<F, E>(&self, f: F) -> Result<&T, E> where
    F: FnOnce() -> Result<T, E>, 
[src]

🔬 This is a nightly-only experimental API. (once_cell #74465)

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

Panics

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

It is an error to reentrantly initialize the cell from f. The exact outcome is unspecified. Current implementation deadlocks, but this may be changed to a panic in the future.

Examples

#![feature(once_cell)]

use std::lazy::SyncOnceCell;

let cell = SyncOnceCell::new();
assert_eq!(cell.get_or_try_init(|| Err(())), Err(()));
assert!(cell.get().is_none());
let value = cell.get_or_try_init(|| -> Result<i32, ()> {
    Ok(92)
});
assert_eq!(value, Ok(&92));
assert_eq!(cell.get(), Some(&92))
Run

pub fn into_inner(self) -> Option<T>[src]

🔬 This is a nightly-only experimental API. (once_cell #74465)

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

Examples

#![feature(once_cell)]

use std::lazy::SyncOnceCell;

let cell: SyncOnceCell<String> = SyncOnceCell::new();
assert_eq!(cell.into_inner(), None);

let cell = SyncOnceCell::new();
cell.set("hello".to_string()).unwrap();
assert_eq!(cell.into_inner(), Some("hello".to_string()));
Run

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

🔬 This is a nightly-only experimental API. (once_cell #74465)

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

Has no effect and returns None if the SyncOnceCell hasn't been initialized.

Safety is guaranteed by requiring a mutable reference.

Examples

#![feature(once_cell)]

use std::lazy::SyncOnceCell;

let mut cell: SyncOnceCell<String> = SyncOnceCell::new();
assert_eq!(cell.take(), None);

let mut cell = SyncOnceCell::new();
cell.set("hello".to_string()).unwrap();
assert_eq!(cell.take(), Some("hello".to_string()));
assert_eq!(cell.get(), None);
Run

Trait Implementations

impl<T: Clone> Clone for SyncOnceCell<T>[src]

impl<T: Debug> Debug for SyncOnceCell<T>[src]

impl<T> Default for SyncOnceCell<T>[src]

impl<T> Drop for SyncOnceCell<T>[src]

impl<T: Eq> Eq for SyncOnceCell<T>[src]

impl<T> From<T> for SyncOnceCell<T>[src]

impl<T: PartialEq> PartialEq<SyncOnceCell<T>> for SyncOnceCell<T>[src]

impl<T: RefUnwindSafe + UnwindSafe> RefUnwindSafe for SyncOnceCell<T>[src]

impl<T: Send> Send for SyncOnceCell<T>[src]

impl<T: Sync + Send> Sync for SyncOnceCell<T>[src]

impl<T: UnwindSafe> UnwindSafe for SyncOnceCell<T>[src]

Auto Trait Implementations

impl<T> Unpin for SyncOnceCell<T> where
    T: Unpin

Blanket Implementations

impl<T> Any for T where
    T: 'static + ?Sized
[src]

impl<T> Borrow<T> for T where
    T: ?Sized
[src]

impl<T> BorrowMut<T> for T where
    T: ?Sized
[src]

impl<T> From<!> for T[src]

impl<T> From<T> for T[src]

impl<T, U> Into<U> for T where
    U: From<T>, 
[src]

impl<T> ToOwned for T where
    T: Clone
[src]

type Owned = T

The resulting type after obtaining ownership.

impl<T, U> TryFrom<U> for T where
    U: Into<T>, 
[src]

type Error = Infallible

The type returned in the event of a conversion error.

impl<T, U> TryInto<U> for T where
    U: TryFrom<T>, 
[src]

type Error = <U as TryFrom<T>>::Error

The type returned in the event of a conversion error.