pub struct LazyLock<T, F = fn() -> T> { /* private fields */ }🔬This is a nightly-only experimental API. (
lazy_cell #109736)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
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§
source§impl<T, F: FnOnce() -> T> LazyLock<T, F>
 
impl<T, F: FnOnce() -> T> LazyLock<T, F>
sourcepub const fn new(f: F) -> LazyLock<T, F>
 🔬This is a nightly-only experimental API. (lazy_cell #109736)
pub const fn new(f: F) -> LazyLock<T, F>
lazy_cell #109736)Creates a new lazy value with the given initializing function.
sourcepub fn into_inner(this: Self) -> Result<T, F>
 🔬This is a nightly-only experimental API. (lazy_cell_consume #109736)
pub fn into_inner(this: Self) -> Result<T, F>
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()));Trait Implementations§
impl<T: RefUnwindSafe + UnwindSafe, F: UnwindSafe> RefUnwindSafe for LazyLock<T, F>
impl<T: Sync + Send, F: Send> Sync for LazyLock<T, F>
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§
source§impl<T> BorrowMut<T> for Twhere
    T: ?Sized,
 
impl<T> BorrowMut<T> for Twhere T: ?Sized,
source§fn borrow_mut(&mut self) -> &mut T
 
fn borrow_mut(&mut self) -> &mut T
Mutably borrows from an owned value. Read more