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.
#![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));
}
Run
🔬This is a nightly-only experimental API. (once_cell
#74465)
Creates a new lazy value with the given initializing
function.
🔬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.
#![feature(once_cell)]
use std::sync::LazyLock;
let lazy = LazyLock::new(|| 92);
assert_eq!(LazyLock::force(&lazy), &92);
assert_eq!(&*lazy, &92);
Run
Formats the value using the given formatter.
Read more
Creates a new lazy value using Default
as the initializing function.
The resulting type after dereferencing.
Dereferences the value.
Executes the destructor for this type.
Read more
Immutably borrows from an owned value.
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Mutably borrows from an owned value.
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Returns the argument unchanged.
Calls U::from(self)
.
That is, this conversion is whatever the implementation of
From<T> for U
chooses to do.
The type returned in the event of a conversion error.
Performs the conversion.
The type returned in the event of a conversion error.
Performs the conversion.