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§

source§

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

source

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

Creates a new lazy value with the given initializing function.

source

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.

source§

impl<T, F: FnOnce() -> T> Lazy<T, F>

source

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::sync::Lazy;

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

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

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 Deref impl, but is explicit.

Example
use once_cell::sync::Lazy;

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

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

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::sync::Lazy;

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

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

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

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

Example
use once_cell::sync::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§

source§

impl<T: Debug, F> Debug for Lazy<T, F>

source§

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

Formats the value using the given formatter. Read more
source§

impl<T: Default> Default for Lazy<T>

source§

fn default() -> Lazy<T>

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

source§

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

§

type Target = T

The resulting type after dereferencing.
source§

fn deref(&self) -> &T

Dereferences the value.
source§

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

source§

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

Mutably dereferences the value.
source§

impl<T, F: RefUnwindSafe> RefUnwindSafe for Lazy<T, F>where
    OnceCell<T>: RefUnwindSafe,

source§

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

Auto Trait Implementations§

§

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

§

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

§

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

Blanket Implementations§

source§

impl<T> Any for Twhere
    T: 'static + ?Sized,

source§

fn type_id(&self) -> TypeId

Gets the TypeId of self. Read more
source§

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

const: unstable · source§

fn borrow(&self) -> &T

Immutably borrows from an owned value. Read more
source§

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
source§

impl<T> From<T> for T

const: unstable · source§

fn from(t: T) -> T

Returns the argument unchanged.

source§

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.

source§

impl<T, U> TryFrom<U> for Twhere
    U: Into<T>,

§

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.
source§

impl<T, U> TryInto<U> for Twhere
    U: TryFrom<T>,

§

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.