Struct std::cell::LazyCell

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pub struct LazyCell<T, F = fn() -> T> { /* private fields */ }

🔬 This is a nightly-only experimental API. (once_cell #74465)

Expand description

A value which is initialized on the first access.

Examples

#![feature(once_cell)]
use std::cell::LazyCell;
let lazy: LazyCell<i32> = LazyCell::new(|| {
 println!("initializing");
 92
});
println!("ready");
println!("{}", *lazy);
println!("{}", *lazy);
// Prints:
// ready
// initializing
// 92
// 92

Run

Implementations

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impl<T, F> LazyCell<T, F>

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pub const fn new(init: F) -> LazyCell<T, F>

🔬 This is a nightly-only experimental API. (once_cell #74465)

Creates a new lazy value with the given initializing function.

Examples

#![feature(once_cell)]
use std::cell::LazyCell;
let hello = "Hello, World!".to_string();
let lazy = LazyCell::new(|| hello.to_uppercase());
assert_eq!(&*lazy, "HELLO, WORLD!");

Run

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impl<T, F> LazyCell<T, F> where
F: FnOnce() -> T,

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pub fn force(this: &LazyCell<T, F>) -> &T

🔬 This is a nightly-only experimental API. (once_cell #74465)

Forces the evaluation of this lazy value and returns a reference to the result.

This is equivalent to the Deref impl, but is explicit.

Examples

#![feature(once_cell)]
use std::cell::LazyCell;
let lazy = LazyCell::new(|| 92);
assert_eq!(LazyCell::force(&lazy), &92);
assert_eq!(&*lazy, &92);

Run

Trait Implementations

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impl<T, F> Debug for LazyCell<T, F> where
T: Debug,

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

Formats the value using the given formatter. Read more

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impl<T> Default for LazyCell<T, fn() -> T> where
T: Default,

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fn default() -> LazyCell<T, fn() -> T>

Creates a new lazy value using Default as the initializing function.

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impl<T, F> Deref for LazyCell<T, F> where
F: FnOnce() -> T,

type Target = T

The resulting type after dereferencing.

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fn deref(&self) -> &T

Dereferences the value.