pub struct OnceCell<T> { /* fields omitted */ }
A cell which can be written to only once. Not thread safe.
Unlike ::std::cell::RefCell
, a OnceCell
provides simple &
references to the contents.
use once_cell::unsync::OnceCell;
let cell = OnceCell::new();
assert!(cell.get().is_none());
let value: &String = cell.get_or_init(|| {
"Hello, World!".to_string()
});
assert_eq!(value, "Hello, World!");
assert!(cell.get().is_some());
INIT: OnceCell<T> = OnceCell{inner: <UnsafeCell>::new(None),}
An empty cell, for initialization in a const
context.
Creates a new empty cell.
Gets the reference to the underlying value. Returns None
if the cell is empty.
Sets the contents of this cell to value
. Returns
Ok(())
if the cell was empty and Err(value)
if it was
full.
use once_cell::unsync::OnceCell;
let cell = OnceCell::new();
assert!(cell.get().is_none());
assert_eq!(cell.set(92), Ok(()));
assert_eq!(cell.set(62), Err(62));
assert!(cell.get().is_some());
Gets the contents of the cell, initializing it with f
if the cell was empty.
use once_cell::unsync::OnceCell;
let cell = OnceCell::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.
use once_cell::unsync::OnceCell;
let cell = OnceCell::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))
Formats the value using the given formatter. Read more
Returns the "default value" for a type. Read more
Performs copy-assignment from source
. Read more