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Struct std::sync::LazyLock

pub struct LazyLock<T, F = fn() -> T> { /* private fields */ }
🔬This is a nightly-only experimental API. (lazy_cell #109736)

A value which is initialized on the first access.

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

Examples

Initialize static variables with LazyLock.

#![feature(lazy_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")
}

Initialize fields with LazyLock.

#![feature(lazy_cell)]

use std::sync::LazyLock;

#[derive(Debug)]
struct UseCellLock {
    number: LazyLock<u32>,
}
fn main() {
    let lock: LazyLock<u32> = LazyLock::new(|| 0u32);

    let data = UseCellLock { number: lock };
    println!("{}", *data.number);
}

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. (lazy_cell #109736)

Creates a new lazy value with the given initializing function.

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pub fn into_inner(this: Self) -> Result<T, F>
🔬This is a nightly-only experimental API. (lazy_cell_consume #109736)

Consumes this LazyLock returning the stored value.

Returns Ok(value) if Lazy is initialized and Err(f) otherwise.

Examples
#![feature(lazy_cell)]
#![feature(lazy_cell_consume)]

use std::sync::LazyLock;

let hello = "Hello, World!".to_string();

let lazy = LazyLock::new(|| hello.to_uppercase());

assert_eq!(&*lazy, "HELLO, WORLD!");
assert_eq!(LazyLock::into_inner(lazy).ok(), Some("HELLO, WORLD!".to_string()));
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pub fn force(this: &LazyLock<T, F>) -> &T
🔬This is a nightly-only experimental API. (lazy_cell #109736)

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(lazy_cell)]

use std::sync::LazyLock;

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

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

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> Drop for LazyLock<T, F>
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fn drop(&mut self)
Executes the destructor for this type. Read more
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impl<T: RefUnwindSafe + UnwindSafe, F: UnwindSafe> RefUnwindSafe for LazyLock<T, F>
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impl<T: Sync + Send, F: Send> Sync for LazyLock<T, F>
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impl<T: UnwindSafe, F: UnwindSafe> UnwindSafe for LazyLock<T, F>

Auto Trait Implementations

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

Blanket Implementations

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impl<T> Any for T
where
    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 T
where
    T: ?Sized,
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fn borrow(&self) -> &T
Immutably borrows from an owned value. Read more
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impl<T> BorrowMut<T> for T
where
    T: ?Sized,
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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
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fn from(t: T) -> T

Returns the argument unchanged.

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impl<T, U> Into<U> for T
where
    U: From<T>,
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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 T
where
    U: Into<T>,
 
type Error = Infallible
The type returned in the event of a conversion error.
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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 T
where
    U: TryFrom<T>,
 
type Error = <U as TryFrom<T>>::Error
The type returned in the event of a conversion error.
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fn try_into(self) -> Result<U, <U as TryFrom<T>>::Error>
Performs the conversion.

© 2010 The Rust Project Developers
Licensed under the Apache License, Version 2.0 or the MIT license, at your option.
https://doc.rust-lang.org/std/sync/struct.LazyLock.html