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 LazyCell, 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: FnOnce() -> T> 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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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>

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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,

Auto Trait Implementations§

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

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

Blanket Implementations§

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impl<T> Any for Twhere T: 'static + ?Sized,

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fn type_id(&self) -> TypeId

Gets the TypeId of self. Read more
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impl<T> Borrow<T> for Twhere T: ?Sized,

const: unstable · source§

fn borrow(&self) -> &T

Immutably borrows from an owned value. Read more
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impl<T> BorrowMut<T> for Twhere T: ?Sized,

const: unstable · source§

fn borrow_mut(&mut self) -> &mut T

Mutably borrows from an owned value. Read more
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impl<T> From<T> for T

const: unstable · source§

fn from(t: T) -> T

Returns the argument unchanged.

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impl<T, U> Into<U> for Twhere U: From<T>,

const: unstable · source§

fn into(self) -> U

Calls U::from(self).

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

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impl<T, U> TryFrom<U> for Twhere U: Into<T>,

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type Error = Infallible

The type returned in the event of a conversion error.
const: unstable · source§

fn try_from(value: U) -> Result<T, <T as TryFrom<U>>::Error>

Performs the conversion.
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impl<T, U> TryInto<U> for Twhere U: TryFrom<T>,

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type Error = <U as TryFrom<T>>::Error

The type returned in the event of a conversion error.
const: unstable · source§

fn try_into(self) -> Result<U, <U as TryFrom<T>>::Error>

Performs the conversion.