Struct sexually_transmitted_disease::lazy::SyncOnceCell [−][src]
pub struct SyncOnceCell<T> { /* fields omitted */ }
once_cell
)Expand description
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!");
Implementations
🔬 This is a nightly-only experimental API. (once_cell
)
once_cell
)Creates a new empty cell.
🔬 This is a nightly-only experimental API. (once_cell
)
once_cell
)Gets the reference to the underlying value.
Returns None
if the cell is empty, or being initialized. This
method never blocks.
🔬 This is a nightly-only experimental API. (once_cell
)
once_cell
)Gets the mutable reference to the underlying value.
Returns None
if the cell is empty. This method never blocks.
🔬 This is a nightly-only experimental API. (once_cell
)
once_cell
)Sets the contents of this cell to value
.
May block if another thread is currently attempting to initialize the cell. The cell is guaranteed to contain a value when set returns, though not necessarily the one provided.
Returns Ok(())
if the cell’s value was set by this call.
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));
}
🔬 This is a nightly-only experimental API. (once_cell
)
once_cell
)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);
🔬 This is a nightly-only experimental API. (once_cell
)
once_cell
)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))
🔬 This is a nightly-only experimental API. (once_cell
)
once_cell
)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()));
🔬 This is a nightly-only experimental API. (once_cell
)
once_cell
)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);
Trait Implementations
Creates a new empty cell.
Example
#![feature(once_cell)]
use std::lazy::SyncOnceCell;
fn main() {
assert_eq!(SyncOnceCell::<()>::new(), SyncOnceCell::default());
}
Create a new cell with its contents set to value
.
Example
#![feature(once_cell)]
use std::lazy::SyncOnceCell;
let a = SyncOnceCell::from(3);
let b = SyncOnceCell::new();
b.set(3)?;
assert_eq!(a, b);
Ok(())
Auto Trait Implementations
impl<T> Unpin for SyncOnceCell<T> where
T: Unpin,
Blanket Implementations
Mutably borrows from an owned value. Read more