pub struct OnceCell<T> { /* fields omitted */ }
A cell which can be written to only once.
Unlike RefCell, a OnceCell only provides shared &T references to its value. Unlike Cell, a OnceCell doesn't require copying or replacing the value to access it.
#![feature(once_cell)]
use std::lazy::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());impl<T> OnceCell<T>[src]
pub fn new() -> OnceCell<T>[src]
Creates a new empty cell.
pub fn get(&self) -> Option<&T>[src]
Gets the reference to the underlying value.
Returns None if the cell is empty.
pub fn get_mut(&mut self) -> Option<&mut T>[src]
Gets the mutable reference to the underlying value.
Returns None if the cell is empty.
pub fn set(&self, value: T) -> Result<(), T>[src]
Sets the contents of the cell to value.
This method returns Ok(()) if the cell was empty and Err(value) if it was full.
#![feature(once_cell)] use std::lazy::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ⓘNotable traits for &'_ mut F
impl<'_, F> Future for &'_ mut F where
    F: Unpin + Future + ?Sized,Â
type Output = <F as Future>::Output;
impl<'_, I> Iterator for &'_ mut I where
    I: Iterator + ?Sized,Â
type Item = <I as Iterator>::Item;
impl<R:Â Read + ?Sized, '_> Read for &'_ mut R
impl<W:Â Write + ?Sized, '_> Write for &'_ mut W
where
    F: FnOnce() -> T, [src]
Gets the contents of the cell, initializing it with f if the cell was empty.
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.
#![feature(once_cell)] use std::lazy::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>, [src]
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.
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.
#![feature(once_cell)]
use std::lazy::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))pub fn into_inner(self) -> Option<T>[src]
Consumes the cell, returning the wrapped value.
Returns None if the cell was empty.
#![feature(once_cell)]
use std::lazy::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()));pub fn take(&mut self) -> Option<T>[src]
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.
Safety is guaranteed by requiring a mutable reference.
#![feature(once_cell)]
use std::lazy::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);impl<T> Clone for OnceCell<T> where
    T: Clone, [src]
impl<T> Debug for OnceCell<T> where
    T: Debug, [src]
impl<T> Default for OnceCell<T>[src]
impl<T> Eq for OnceCell<T> where
    T: Eq, [src]
impl<T> From<T> for OnceCell<T>[src]
impl<T> PartialEq<OnceCell<T>> for OnceCell<T> where
    T: PartialEq<T>, [src]
impl<T> !RefUnwindSafe for OnceCell<T>impl<T> Send for OnceCell<T> where
    T: Send, impl<T> !Sync for OnceCell<T>impl<T> Unpin for OnceCell<T> where
    T: Unpin, impl<T> UnwindSafe for OnceCell<T> where
    T: UnwindSafe, impl<T> Any for T where
    T: 'static + ?Sized, [src]
impl<T> Borrow<T> for T where
    T: ?Sized, [src]
fn borrow(&self) -> &TⓘNotable traits for &'_ mut F
impl<'_, F> Future for &'_ mut F where
    F: Unpin + Future + ?Sized,Â
type Output = <F as Future>::Output;
impl<'_, I> Iterator for &'_ mut I where
    I: Iterator + ?Sized,Â
type Item = <I as Iterator>::Item;
impl<R:Â Read + ?Sized, '_> Read for &'_ mut R
impl<W:Â Write + ?Sized, '_> Write for &'_ mut W
[src]
impl<T> BorrowMut<T> for T where
    T: ?Sized, [src]
fn borrow_mut(&mut self) -> &mut TⓘNotable traits for &'_ mut F
impl<'_, F> Future for &'_ mut F where
    F: Unpin + Future + ?Sized,Â
type Output = <F as Future>::Output;
impl<'_, I> Iterator for &'_ mut I where
    I: Iterator + ?Sized,Â
type Item = <I as Iterator>::Item;
impl<R:Â Read + ?Sized, '_> Read for &'_ mut R
impl<W:Â Write + ?Sized, '_> Write for &'_ mut W
[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 = TThe resulting type after obtaining ownership.
fn to_owned(&self) -> T[src]
fn clone_into(&self, target: &mut T)[src]
impl<T, U> TryFrom<U> for T where
    U: Into<T>, [src]
type Error = InfallibleThe type returned in the event of a conversion error.
fn try_from(value: U) -> Result<T, <T as TryFrom<U>>::Error>[src]
impl<T, U> TryInto<U> for T where
    U: TryFrom<T>, [src]
© 2010 The Rust Project Developers
Licensed under the Apache License, Version 2.0 or the MIT license, at your option.
https://doc.rust-lang.org/std/lazy/struct.OnceCell.html