Struct OnceCell 

pub struct OnceCell<T>(/* private fields */);

A cell which can only be initialized once.

Like crate::sync::OnceLock, but not thread-safe.

Implementations

impl<T> OnceCell<T>

pub const fn new() -> OnceCell<T>

Create an uninitialized cell.

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

Get a reference to the current value, or None if uninitialized.

pub fn get_or_init(&self, func: impl FnOnce() -> T) -> &T

Get a reference to the current value if initialed, invoking the specified callback otherwise.

pub fn get_or_try_init<E>( &self, func: impl FnOnce() -> Result<T, E>, ) -> Result<&T, E>

Get a reference to the current value if initialized, invoking the specified callback otherwise.

Errors

Any errors from callback function will be propagated upwards, and in that case the cell will remain unchanged.

pub fn set(&self, value: T) -> Result<(), T>

Initializes the contents of the cell to value, returning an error if already initialized to some other value.

Errors

Returns Ok(()) if successfully initialized, or Err(given_Value) if already initialized.

pub fn take(&mut self) -> Option<T>

Takes the value out of this OnceCell, moving it back to an uninitialized state.

Returns None if not currently initialized.

This is safe because it takes a mutable reference.

pub fn into_inner(self) -> Option<T>

Consumes the cell, returning the wrapped value (if any).

Trait Implementations

impl<T: Clone> Clone for OnceCell<T>

fn clone(&self) -> Self

Returns a duplicate of the value.

fn clone_from(&mut self, source: &Self)

Performs copy-assignment from source.

impl<T: Debug> Debug for OnceCell<T>

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

Formats the value using the given formatter.

impl<T> Default for OnceCell<T>

fn default() -> Self

Returns the “default value” for a type.

impl<T> From<T> for OnceCell<T>

fn from(value: T) -> Self

Converts to this type from the input type.

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