Struct once_cell::sync::Lazy

source · [−]
pub struct Lazy<T, F = fn() -> T> { /* private fields */ }
Expand description

A value which is initialized on the first access.

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

Example

use std::collections::HashMap;

use once_cell::sync::Lazy;

static HASHMAP: Lazy<HashMap<i32, String>> = Lazy::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")
}

Implementations

Creates a new lazy value with the given initializing function.

Consumes this Lazy returning the stored value.

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

Forces the evaluation of this lazy value and returns a reference to the result. This is equivalent to the Deref impl, but is explicit.

Example
use once_cell::sync::Lazy;

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

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

Trait Implementations

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.

Mutably dereferences the value.

Auto Trait Implementations

Blanket Implementations

Gets the TypeId of self. Read more

Immutably borrows from an owned value. Read more

Mutably borrows from an owned value. Read more

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.