Creates a new empty cell.

Gets the reference to the underlying value.

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

Gets the mutable reference to the underlying value.

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

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));
}

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);

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))

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()));

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);