Struct OnceLock 

pub struct OnceLock<T, O: Once> { /* private fields */ }

A synchronization primitive which can nominally be written to only once.

Implementations

impl<T, O: Once> OnceLock<T, O>

pub fn new() -> Self

Creates a new empty cell.

pub fn get(&self) -> Option<&T>

Gets the reference to the underlying value.

Returns None if the cell is empty, or being initialized. This method never blocks.

pub fn get_or_init<F: FnOnce() -> T>(&self, f: F) -> &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

Panics if f panics. If f panics, the cell is left uninitialized and subsequent attempts to initialize the cell are expected to panic.

Trait Implementations

impl<T: Debug, O: Once> Debug for OnceLock<T, O>

fn fmt(&self, f: &mut Formatter<'_>) -> Result

Formats the value using the given formatter.

impl<T, O: Once> Default for OnceLock<T, O>

fn default() -> Self

Returns the “default value” for a type.

impl<T, O: Once> Drop for OnceLock<T, O>

fn drop(&mut self)

Executes the destructor for this type.

fn pin_drop(self: Pin<&mut Self>)

🔬This is a nightly-only experimental API. (pin_ergonomics)

Execute the destructor for this type, but different to Drop::drop, it requires self to be pinned.

impl<T: Eq, O: Once> Eq for OnceLock<T, O>

impl<T: PartialEq, O: Once> PartialEq for OnceLock<T, O>

fn eq(&self, other: &Self) -> bool

Equality operator ==.

fn ne(&self, other: &Rhs) -> bool

Inequality operator !=.

impl<T: Send, O: Once> Send for OnceLock<T, O>

impl<T: Send + Sync, O: Once> Sync for OnceLock<T, O>