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

A value which is initialized on the first access.

Example

use once_cell::unsync::Lazy;

let lazy: Lazy<i32> = Lazy::new(|| {
    println!("initializing");
    92
});
println!("ready");
println!("{}", *lazy);
println!("{}", *lazy);

// Prints:
//   ready
//   initializing
//   92
//   92

Implementations

Creates a new lazy value with the given initializing function.

Example
use once_cell::unsync::Lazy;

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

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

assert_eq!(&*lazy, "HELLO, WORLD!");

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::unsync::Lazy;

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

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

Forces the evaluation of this lazy value and returns a mutable reference to the result.

This is equivalent to the DerefMut impl, but is explicit.

Example
use once_cell::unsync::Lazy;

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

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

Gets the reference to the result of this lazy value if it was initialized, otherwise returns None.

Example
use once_cell::unsync::Lazy;

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

assert_eq!(Lazy::get(&lazy), None);
assert_eq!(&*lazy, &92);
assert_eq!(Lazy::get(&lazy), Some(&92));

Gets the mutable reference to the result of this lazy value if it was initialized, otherwise returns None.

Example
use once_cell::unsync::Lazy;

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

assert_eq!(Lazy::get_mut(&mut lazy), None);
assert_eq!(*lazy, 92);
assert_eq!(Lazy::get_mut(&mut lazy), Some(&mut 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.