Struct alloc_data::prelude::sync::LazyLock

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

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

A value which is initialized on the first access.

This type is a thread-safe Lazy, and can be used in statics.

Examples

#![feature(once_cell)]

use std::collections::HashMap;

use std::sync::LazyLock;

static HASHMAP: LazyLock<HashMap<i32, String>> = LazyLock::new(|| {
    println!("initializing");
    let mut m = HashMap::new();
    m.insert(13, "Spica".to_string());
    m.insert(74, "Hoyten".to_string());
    m
});

fn main() {
    println!("ready");
    std::thread::spawn(|| {
        println!("{:?}", HASHMAP.get(&13));
    }).join().unwrap();
    println!("{:?}", HASHMAP.get(&74));

    // Prints:
    //   ready
    //   initializing
    //   Some("Spica")
    //   Some("Hoyten")
}

Implementations

impl<T, F> LazyLock<T, F>

pub const fn new(f: F) -> LazyLock<T, F>

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

Creates a new lazy value with the given initializing function.

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

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

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

Forces the evaluation of this lazy value and returns a reference to result. This is equivalent to the Deref impl, but is explicit.

Examples

#![feature(once_cell)]

use std::sync::LazyLock;

let lazy = LazyLock::new(|| 92);

assert_eq!(LazyLock::force(&lazy), &92);
assert_eq!(&*lazy, &92);

Trait Implementations

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

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

Formats the value using the given formatter.

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

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

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

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

type Target = T

The resulting type after dereferencing.

fn deref(&self) -> &T

Dereferences the value.

impl<T, F> RefUnwindSafe for LazyLock<T, F> where
    F: UnwindSafe,
    OnceLock<T>: RefUnwindSafe, 

impl<T, F> Sync for LazyLock<T, F> where
    F: Send,
    OnceLock<T>: Sync, 

impl<T, F> UnwindSafe for LazyLock<T, F> where
    F: UnwindSafe,
    OnceLock<T>: UnwindSafe,