[][src]Struct once_cell::unsync::OnceCell

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.

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());

Methods

impl<T> OnceCell<T>[src]

pub const 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 set(&self, value: T) -> Result<(), T>[src]

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: FnOnce() -> T>(&self, f: F) -> &T[src]

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: FnOnce() -> Result<T, E>, E>(
    &self,
    f: F
) -> 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.

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))

pub fn into_inner(self) -> Option<T>[src]

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> From<T> for OnceCell<T>[src]

impl<T: PartialEq> PartialEq<OnceCell<T>> for OnceCell<T>[src]

#[must_use] fn ne(&self, other: &Rhs) -> bool1.0.0[src]

This method tests for !=.

impl<T> Default for OnceCell<T>[src]

impl<T: Clone> Clone for OnceCell<T>[src]

fn clone_from(&mut self, source: &Self)1.0.0[src]

Performs copy-assignment from source. Read more

impl<T: Debug> Debug for OnceCell<T>[src]

impl<T: UnwindSafe> UnwindSafe for OnceCell<T>[src]

impl<T: RefUnwindSafe + UnwindSafe> RefUnwindSafe for OnceCell<T>[src]

Auto Trait Implementations

impl<T> Send for OnceCell<T> where
    T: Send

impl<T> Unpin for OnceCell<T> where
    T: Unpin

impl<T> !Sync for OnceCell<T>

Blanket Implementations

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 = T

The resulting type after obtaining ownership.

impl<T, U> TryFrom<U> for T where
    U: Into<T>, 
[src]

type Error = Infallible

The type returned in the event of a conversion error.

impl<T, U> TryInto<U> for T where
    U: TryFrom<T>, 
[src]

type Error = <U as TryFrom<T>>::Error

The type returned in the event of a conversion error.

impl<T> Borrow<T> for T where
    T: ?Sized
[src]

impl<T> BorrowMut<T> for T where
    T: ?Sized
[src]

impl<T> Any for T where
    T: 'static + ?Sized
[src]