pub struct LazyCell<T, F = fn() -> T> {
    state: UnsafeCell<State<T, F>>,
}
🔬This is a nightly-only experimental API. (lazy_cell #109736)
Expand description

A value which is initialized on the first access.

For a thread-safe version of this struct, see std::sync::LazyLock.

§Examples

#![feature(lazy_cell)]

use std::cell::LazyCell;

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

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

Fields§

§state: UnsafeCell<State<T, F>>
🔬This is a nightly-only experimental API. (lazy_cell #109736)

Implementations§

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impl<T, F> LazyCell<T, F>
where F: FnOnce() -> T,

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pub const fn new(f: F) -> LazyCell<T, F>

🔬This is a nightly-only experimental API. (lazy_cell #109736)

Creates a new lazy value with the given initializing function.

§Examples
#![feature(lazy_cell)]

use std::cell::LazyCell;

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

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

assert_eq!(&*lazy, "HELLO, WORLD!");
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pub fn into_inner(this: LazyCell<T, F>) -> Result<T, F>

🔬This is a nightly-only experimental API. (lazy_cell_consume #109736)

Consumes this LazyCell 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::cell::LazyCell;

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

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

assert_eq!(&*lazy, "HELLO, WORLD!");
assert_eq!(LazyCell::into_inner(lazy).ok(), Some("HELLO, WORLD!".to_string()));
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pub fn force(this: &LazyCell<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 the result.

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

§Examples
#![feature(lazy_cell)]

use std::cell::LazyCell;

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

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

Trait Implementations§

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impl<T, F> Debug for LazyCell<T, F>
where T: Debug,

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fn fmt(&self, f: &mut Formatter<'_>) -> Result<(), Error>

Formats the value using the given formatter. Read more
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impl<T> Default for LazyCell<T>
where T: Default,

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fn default() -> LazyCell<T>

Creates a new lazy value using Default as the initializing function.

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impl<T, F> Deref for LazyCell<T, F>
where F: FnOnce() -> T,

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type Target = T

The resulting type after dereferencing.
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fn deref(&self) -> &T

Dereferences the value.

Auto Trait Implementations§

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impl<T, F = fn() -> T> !Freeze for LazyCell<T, F>

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impl<T, F = fn() -> T> !RefUnwindSafe for LazyCell<T, F>

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impl<T, F> Send for LazyCell<T, F>
where F: Send, T: Send,

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impl<T, F = fn() -> T> !Sync for LazyCell<T, F>

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impl<T, F> Unpin for LazyCell<T, F>
where F: Unpin, T: Unpin,

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impl<T, F> UnwindSafe for LazyCell<T, F>
where F: UnwindSafe, T: UnwindSafe,

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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>,

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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>,

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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.