Struct mitochondria::OnceCell

pub struct OnceCell<T>(_);

A mutable memory location that can be set only once.

Methods

impl<T> OnceCell<T>

fn new() -> Self

Creates a new OnceCell.

Examples

use mitochondria::OnceCell;

let c = OnceCell::<String>::new();

fn new_with_value(value: T) -> Self

Creates a new OnceCell initialised with value.

Examples

use mitochondria::OnceCell;

let c = OnceCell::new_with_value(Some("Hello vesicle!".to_owned()));

fn try_init_once<E, F>(&self, f: F) -> Result<&T, E> where F: FnOnce() -> Result<T, E>

Calls a function to try to initialize this cell.

If the cell was already-initialized, the function is not called. Otherwise, if the function returns Ok(value), the cell is initialized with value.

This method returns None if the cell could not be initialized, or Some(&value) otherwise.

Examples

use mitochondria::OnceCell;

let c = OnceCell::new();

assert_eq!(c.try_init_once(|| Err(())), Err(()));

let greeting = c.try_init_once::<(), _>(|| {
    Ok("Hello ribosome!".to_owned())
}).unwrap();

use mitochondria::OnceCell;

let c = OnceCell::new_with_value("Hello reticulum!".to_owned());

// Calls to `try_init_once` on initialized cells are ignored.
assert_eq!(
    c.try_init_once::<(), _>(|| Ok("Goodbye!".to_owned())).unwrap(),
    "Hello reticulum!");

fn as_ref(&self) -> Option<&T>

Returns None if the cell is not initialised, or else returns a reference to the value wrapped in Some.

Examples

use mitochondria::OnceCell;

let c = OnceCell::new();

assert!(c.as_ref().is_none());

let greeting = c.init_once(|| "Hello nucleus!".to_owned());
assert_eq!(c.as_ref(), Some(greeting));

fn as_mut(&mut self) -> Option<&mut T>

Returns None if the cell is not initialised, or else returns a mutable reference to the value wrapped in Some.

This call borrows OnceCell mutably (at compile-time) which guarantees that we possess the only reference.

Examples

use mitochondria::OnceCell;

let mut c = OnceCell::new();

assert!(c.as_mut().is_none());

c.init_once(|| "Nucleo".to_owned());
*c.as_mut().unwrap() += "lus!";
assert_eq!(c.as_ref().unwrap(), "Nucleolus!");

impl<T> OnceCell<T>

fn init_once<F>(&self, f: F) -> &T where F: FnOnce() -> T

Calls a function to initialize this cell and borrows its value.

If the cell was already-initialized, the function is not called and the returned value is the one that was already there.

Examples

use mitochondria::OnceCell;

let c = OnceCell::new();

let greeting: &str = c.init_once(|| "Hello ribosome!".to_owned());

use mitochondria::OnceCell;

let c = OnceCell::new_with_value("Hello reticulum!".to_owned());

// Calls to `init_once` on initialized cells are ignored.
assert_eq!(
    c.init_once(|| "Goodbye!".to_owned()),
    "Hello reticulum!");

Trait Implementations

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

impl<T: Clone> Clone for OnceCell<T>

fn clone(&self) -> Self

Returns a copy 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

Performs the conversion.