Struct std::lazy::SyncOnceCell [−][src]
pub struct SyncOnceCell<T> { /* fields omitted */ }
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!");Run
Implementations
impl<T> SyncOnceCell<T>
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impl<T> SyncOnceCell<T>
[src]pub const fn new() -> SyncOnceCell<T>
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Creates a new empty cell.
pub fn get(&self) -> Option<&T>
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Gets the reference to the underlying value.
Returns None
if the cell is empty, or being initialized. This
method never blocks.
pub fn get_mut(&mut self) -> Option<&mut T>
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Gets the mutable reference to the underlying value.
Returns None
if the cell is empty. This method never blocks.
pub fn set(&self, value: T) -> Result<(), T>
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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)); }Run
pub fn get_or_init<F>(&self, f: F) -> &TⓘNotable traits for &'_ mut F
impl<'_, F> Future for &'_ mut F where
F: Future + Unpin + ?Sized, type Output = <F as Future>::Output;impl<'_, I> Iterator for &'_ mut I where
I: Iterator + ?Sized, type Item = <I as Iterator>::Item;impl<R: Read + ?Sized> Read for &mut Rimpl<W: Write + ?Sized> Write for &mut W
where
F: FnOnce() -> T,
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Notable traits for &'_ mut F
impl<'_, F> Future for &'_ mut F where
F: Future + Unpin + ?Sized, type Output = <F as Future>::Output;impl<'_, I> Iterator for &'_ mut I where
I: Iterator + ?Sized, type Item = <I as Iterator>::Item;impl<R: Read + ?Sized> Read for &mut Rimpl<W: Write + ?Sized> Write for &mut W
F: FnOnce() -> T,
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);Run
pub fn get_or_try_init<F, E>(&self, f: F) -> Result<&T, E> where
F: FnOnce() -> Result<T, E>,
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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
.
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))Run
pub fn into_inner(self) -> Option<T>
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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()));Run
pub fn take(&mut self) -> Option<T>
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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);Run
Trait Implementations
impl<T: Clone> Clone for SyncOnceCell<T>
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impl<T: Clone> Clone for SyncOnceCell<T>
[src]fn clone(&self) -> SyncOnceCell<T>
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pub fn clone_from(&mut self, source: &Self)
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impl<T> Default for SyncOnceCell<T>
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impl<T> Default for SyncOnceCell<T>
[src]fn default() -> SyncOnceCell<T>
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impl<T> Drop for SyncOnceCell<T>
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impl<T> Drop for SyncOnceCell<T>
[src]impl<T> From<T> for SyncOnceCell<T>
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impl<T> From<T> for SyncOnceCell<T>
[src]impl<T: PartialEq> PartialEq<SyncOnceCell<T>> for SyncOnceCell<T>
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impl<T: PartialEq> PartialEq<SyncOnceCell<T>> for SyncOnceCell<T>
[src]impl<T: Eq> Eq for SyncOnceCell<T>
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impl<T: RefUnwindSafe + UnwindSafe> RefUnwindSafe for SyncOnceCell<T>
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impl<T: Send> Send for SyncOnceCell<T>
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impl<T: Sync + Send> Sync for SyncOnceCell<T>
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impl<T: UnwindSafe> UnwindSafe for SyncOnceCell<T>
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Auto Trait Implementations
impl<T> Unpin for SyncOnceCell<T> where
T: Unpin,
T: Unpin,
Blanket Implementations
impl<T> Borrow<T> for T where
T: ?Sized,
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impl<T> Borrow<T> for T where
T: ?Sized,
[src]pub fn borrow(&self) -> &TⓘNotable traits for &'_ mut F
impl<'_, F> Future for &'_ mut F where
F: Future + Unpin + ?Sized, type Output = <F as Future>::Output;impl<'_, I> Iterator for &'_ mut I where
I: Iterator + ?Sized, type Item = <I as Iterator>::Item;impl<R: Read + ?Sized> Read for &mut Rimpl<W: Write + ?Sized> Write for &mut W
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Notable traits for &'_ mut F
impl<'_, F> Future for &'_ mut F where
F: Future + Unpin + ?Sized, type Output = <F as Future>::Output;impl<'_, I> Iterator for &'_ mut I where
I: Iterator + ?Sized, type Item = <I as Iterator>::Item;impl<R: Read + ?Sized> Read for &mut Rimpl<W: Write + ?Sized> Write for &mut W
impl<T> BorrowMut<T> for T where
T: ?Sized,
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impl<T> BorrowMut<T> for T where
T: ?Sized,
[src]pub fn borrow_mut(&mut self) -> &mut TⓘNotable traits for &'_ mut F
impl<'_, F> Future for &'_ mut F where
F: Future + Unpin + ?Sized, type Output = <F as Future>::Output;impl<'_, I> Iterator for &'_ mut I where
I: Iterator + ?Sized, type Item = <I as Iterator>::Item;impl<R: Read + ?Sized> Read for &mut Rimpl<W: Write + ?Sized> Write for &mut W
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Notable traits for &'_ mut F
impl<'_, F> Future for &'_ mut F where
F: Future + Unpin + ?Sized, type Output = <F as Future>::Output;impl<'_, I> Iterator for &'_ mut I where
I: Iterator + ?Sized, type Item = <I as Iterator>::Item;impl<R: Read + ?Sized> Read for &mut Rimpl<W: Write + ?Sized> Write for &mut W