Struct core::cell::lazy::LazyCell

source ·
pub struct LazyCell<T, F = fn() -> T> {
    cell: OnceCell<T>,
    init: Cell<Option<F>>,
}
🔬This is a nightly-only experimental API. (once_cell #74465)
Expand description

A value which is initialized on the first access.

For a thread-safe version of this struct, see std::sync::LazyLock.

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

Fields§

§cell: OnceCell<T>
🔬This is a nightly-only experimental API. (once_cell #74465)
§init: Cell<Option<F>>
🔬This is a nightly-only experimental API. (once_cell #74465)

Implementations§

🔬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
🔬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§

Formats the value using the given formatter. Read more

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

The resulting type after dereferencing.
Dereferences the value.

Auto Trait Implementations§

Blanket Implementations§

Gets the TypeId of self. Read more
Immutably borrows from an owned value. Read more
Mutably borrows from an owned value. Read more

Returns the argument unchanged.

Calls U::from(self).

That is, this conversion is whatever the implementation of From<T> for U chooses to do.

🔬This is a nightly-only experimental API. (sized_type_properties)
true if this type requires no storage. false if its size is greater than zero. Read more
The type returned in the event of a conversion error.
Performs the conversion.
The type returned in the event of a conversion error.
Performs the conversion.