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§

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impl<T, F> Lazy<T, F>

pub const fn new(init: F) -> Lazy<T, F>

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!");

pub fn into_value(this: Lazy<T, F>) -> Result<T, F>

Consumes this Lazy returning the stored value.

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

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

pub fn force(this: &Lazy<T, F>) -> &T

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);

pub fn force_mut(this: &mut Lazy<T, F>) -> &mut T

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);

pub fn get(this: &Lazy<T, F>) -> Option<&T>

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));

pub fn get_mut(this: &mut Lazy<T, F>) -> Option<&mut T>

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§

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impl<T, F> Debug for Lazy<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 Lazy<T, fn() -> T>where T: Default,

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fn default() -> Lazy<T, fn() -> T>

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

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impl<T, F> Deref for Lazy<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.
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impl<T, F> DerefMut for Lazy<T, F>where F: FnOnce() -> T,

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fn deref_mut(&mut self) -> &mut T

Mutably dereferences the value.
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impl<T, F> RefUnwindSafe for Lazy<T, F>where F: RefUnwindSafe, OnceCell<T>: RefUnwindSafe,

Auto Trait Implementations§

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

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

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

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

Blanket Implementations§

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impl<T> Any for Twhere 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 Twhere T: ?Sized,

const: unstable · source§

fn borrow(&self) -> &T

Immutably borrows from an owned value. Read more
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impl<T> BorrowMut<T> for Twhere T: ?Sized,

const: unstable · source§

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

const: unstable · source§

fn from(t: T) -> T

Returns the argument unchanged.

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impl<T> Instrument for T

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fn instrument(self, span: Span) -> Instrumented<Self>

Instruments this type with the provided Span, returning an Instrumented wrapper. Read more
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fn in_current_span(self) -> Instrumented<Self>

Instruments this type with the current Span, returning an Instrumented wrapper. Read more
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impl<T, U> Into<U> for Twhere U: From<T>,

const: unstable · source§

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> Same<T> for T

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type Output = T

Should always be Self
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impl<T, U> TryFrom<U> for Twhere U: Into<T>,

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type Error = Infallible

The type returned in the event of a conversion error.
const: unstable · source§

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 Twhere U: TryFrom<T>,

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type Error = <U as TryFrom<T>>::Error

The type returned in the event of a conversion error.
const: unstable · source§

fn try_into(self) -> Result<U, <U as TryFrom<T>>::Error>

Performs the conversion.
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impl<V, T> VZip<V> for Twhere V: MultiLane<T>,

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fn vzip(self) -> V

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impl<T> WithSubscriber for T

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fn with_subscriber<S>(self, subscriber: S) -> WithDispatch<Self>where S: Into<Dispatch>,

Attaches the provided Subscriber to this type, returning a WithDispatch wrapper. Read more
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fn with_current_subscriber(self) -> WithDispatch<Self>

Attaches the current default Subscriber to this type, returning a WithDispatch wrapper. Read more