Struct diem_sdk::crypto::_once_cell::unsync::OnceCell [−]
pub struct OnceCell<T> { /* fields omitted */ }
Expand description
A cell which can be written to only once. It is not thread safe.
Unlike std::cell::RefCell
, a OnceCell
provides simple &
references to the contents.
Example
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());
Implementations
impl<T> OnceCell<T>
impl<T> OnceCell<T>
Gets a reference to the underlying value.
Returns None
if the cell is empty.
Gets a mutable 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.
Example
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());
pub fn get_or_init<F>(&self, f: F) -> &T where
F: FnOnce() -> T,
pub fn get_or_init<F>(&self, f: F) -> &T where
F: FnOnce() -> T,
Gets the contents of the cell, initializing it with f
if the cell was empty.
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
. Doing
so results in a panic.
Example
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);
pub fn get_or_try_init<F, E>(&self, f: F) -> Result<&T, E> where
F: FnOnce() -> Result<T, E>,
pub fn get_or_try_init<F, E>(&self, f: F) -> Result<&T, E> where
F: FnOnce() -> Result<T, E>,
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
. Doing
so results in a panic.
Example
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))
Takes the value out of this OnceCell
, moving it back to an uninitialized state.
Has no effect and returns None
if the OnceCell
hasn’t been initialized.
Examples
use once_cell::unsync::OnceCell;
let mut cell: OnceCell<String> = OnceCell::new();
assert_eq!(cell.take(), None);
let mut cell = OnceCell::new();
cell.set("hello".to_string()).unwrap();
assert_eq!(cell.take(), Some("hello".to_string()));
assert_eq!(cell.get(), None);
pub fn into_inner(self) -> Option<T>
pub fn into_inner(self) -> Option<T>
Consumes the OnceCell
, returning the wrapped value.
Returns None
if the cell was empty.
Examples
use once_cell::unsync::OnceCell;
let cell: OnceCell<String> = OnceCell::new();
assert_eq!(cell.into_inner(), None);
let cell = OnceCell::new();
cell.set("hello".to_string()).unwrap();
assert_eq!(cell.into_inner(), Some("hello".to_string()));
Trait Implementations
impl<T> RefUnwindSafe for OnceCell<T> where
T: RefUnwindSafe + UnwindSafe,
impl<T> UnwindSafe for OnceCell<T> where
T: UnwindSafe,
Auto Trait Implementations
Blanket Implementations
Mutably borrows from an owned value. Read more
Compare self to key
and return true
if they are equal.
Instruments this type with the provided Span
, returning an
Instrumented
wrapper. Read more
pub fn vzip(self) -> V
Attaches the provided Subscriber
to this type, returning a
WithDispatch
wrapper. Read more
Attaches the current default Subscriber
to this type, returning a
WithDispatch
wrapper. Read more