Struct mitochondria::OnceCell

pub struct OnceCell<T>(_);

A mutable memory location that can be set only once.

Methods

impl<T> OnceCell<T>

fn new(value: Option<T>) -> Self

Creates a new OnceCell that may already be initialized.

Example

use mitochondria::OnceCell;

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

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

Performs an initialization routine once and only once. The given closure will be executed if this is the first time init_once has been called, and otherwise the routine will not be invoked.

The result of the given closure is then used to set the contents of this cell and borrowed as the return value of this method.

Examples

use mitochondria::OnceCell;

let c = OnceCell::new(None);

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

use mitochondria::OnceCell;

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

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

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

Borrows the contained value, if initialized.

Examples

use mitochondria::OnceCell;

let c = OnceCell::new(None);

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

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