Struct std::sync::LazyLock

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pub struct LazyLock<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.

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")
}

Run

Implementations

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

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

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

Creates a new lazy value with the given initializing function.

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

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pub fn force(this: &LazyLock<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 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);

Run

Trait Implementations

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

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

Formats the value using the given formatter. Read more

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impl<T: Default> Default for LazyLock<T>

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fn default() -> LazyLock<T>

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

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

type Target = T

The resulting type after dereferencing.

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fn deref(&self) -> &T

Dereferences the value.

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

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

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