wasmer_types::lib::std::sync

Struct LazyLock

1.80.0 · Source
pub struct LazyLock<T, F = fn() -> T> { /* private fields */ }
Available on crate feature std only.
Expand description

A value which is initialized on the first access.

This type is a thread-safe LazyCell, and can be used in statics. Since initialization may be called from multiple threads, any dereferencing call will block the calling thread if another initialization routine is currently running.

§Examples

Initialize static variables with LazyLock.

use std::sync::LazyLock;

// n.b. static items do not call [`Drop`] on program termination, so this won't be deallocated.
// this is fine, as the OS can deallocate the terminated program faster than we can free memory
// but tools like valgrind might report "memory leaks" as it isn't obvious this is intentional.
static DEEP_THOUGHT: LazyLock<String> = LazyLock::new(|| {
    // M3 Ultra takes about 16 million years in --release config
    another_crate::great_question()
});

// The `String` is built, stored in the `LazyLock`, and returned as `&String`.
let _ = &*DEEP_THOUGHT;

Initialize fields with LazyLock.

use std::sync::LazyLock;

#[derive(Debug)]
struct UseCellLock {
    number: LazyLock<u32>,
}
fn main() {
    let lock: LazyLock<u32> = LazyLock::new(|| 0u32);

    let data = UseCellLock { number: lock };
    println!("{}", *data.number);
}

Implementations§

Source§

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

1.80.0 (const: 1.80.0) · Source

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

Creates a new lazy value with the given initializing function.

§Examples
use std::sync::LazyLock;

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

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

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

pub fn into_inner(this: LazyLock<T, F>) -> Result<T, F>

🔬This is a nightly-only experimental API. (lazy_cell_into_inner)

Consumes this LazyLock returning the stored value.

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

§Examples
#![feature(lazy_cell_into_inner)]

use std::sync::LazyLock;

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

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

assert_eq!(&*lazy, "HELLO, WORLD!");
assert_eq!(LazyLock::into_inner(lazy).ok(), Some("HELLO, WORLD!".to_string()));
Source

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

🔬This is a nightly-only experimental API. (lazy_get)

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

§Examples
#![feature(lazy_get)]
use std::sync::LazyLock;

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

let p = LazyLock::force_mut(&mut lazy);
assert_eq!(*p, 92);
*p = 44;
assert_eq!(*lazy, 44);
1.80.0 · Source

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

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

This method will block the calling thread if another initialization routine is currently running.

§Examples
use std::sync::LazyLock;

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

assert_eq!(LazyLock::force(&lazy), &92);
assert_eq!(&*lazy, &92);
Source§

impl<T, F> LazyLock<T, F>

Source

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

🔬This is a nightly-only experimental API. (lazy_get)

Returns a mutable reference to the value if initialized, or None if not.

§Examples
#![feature(lazy_get)]

use std::sync::LazyLock;

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

assert_eq!(LazyLock::get_mut(&mut lazy), None);
let _ = LazyLock::force(&lazy);
*LazyLock::get_mut(&mut lazy).unwrap() = 44;
assert_eq!(*lazy, 44);
Source

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

🔬This is a nightly-only experimental API. (lazy_get)

Returns a reference to the value if initialized, or None if not.

§Examples
#![feature(lazy_get)]

use std::sync::LazyLock;

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

assert_eq!(LazyLock::get(&lazy), None);
let _ = LazyLock::force(&lazy);
assert_eq!(LazyLock::get(&lazy), Some(&92));

Trait Implementations§

1.80.0 · Source§

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

Source§

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

Formats the value using the given formatter. Read more
1.80.0 · Source§

impl<T> Default for LazyLock<T>
where T: Default,

Source§

fn default() -> LazyLock<T>

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

1.80.0 · Source§

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

Source§

fn deref(&self) -> &T

Dereferences the value.

This method will block the calling thread if another initialization routine is currently running.

Source§

type Target = T

The resulting type after dereferencing.
1.80.0 · Source§

impl<T, F> Drop for LazyLock<T, F>

Source§

fn drop(&mut self)

Executes the destructor for this type. Read more
1.80.0 · Source§

impl<T, F> RefUnwindSafe for LazyLock<T, F>

1.80.0 · Source§

impl<T, F> Sync for LazyLock<T, F>
where T: Sync + Send, F: Send,

1.80.0 · Source§

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

Auto Trait Implementations§

§

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

§

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

§

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

Blanket Implementations§

Source§

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

Source§

fn type_id(&self) -> TypeId

Gets the TypeId of self. Read more
Source§

impl<T> ArchivePointee for T

Source§

type ArchivedMetadata = ()

The archived version of the pointer metadata for this type.
Source§

fn pointer_metadata( _: &<T as ArchivePointee>::ArchivedMetadata, ) -> <T as Pointee>::Metadata

Converts some archived metadata to the pointer metadata for itself.
Source§

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

Source§

fn borrow(&self) -> &T

Immutably borrows from an owned value. Read more
Source§

impl<T> BorrowMut<T> for T
where T: ?Sized,

Source§

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

Mutably borrows from an owned value. Read more
Source§

impl<T> From<T> for T

Source§

fn from(t: T) -> T

Returns the argument unchanged.

Source§

impl<T, U> Into<U> for T
where U: From<T>,

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> LayoutRaw for T

Source§

fn layout_raw(_: <T as Pointee>::Metadata) -> Result<Layout, LayoutError>

Returns the layout of the type.
Source§

impl<T> Pointee for T

Source§

type Metadata = ()

The metadata type for pointers and references to this type.
Source§

impl<P, T> Receiver for P
where P: Deref<Target = T> + ?Sized, T: ?Sized,

Source§

type Target = T

🔬This is a nightly-only experimental API. (arbitrary_self_types)
Available on non-bootstrap only.
The target type on which the method may be called.
Source§

impl<T> Same for T

Source§

type Output = T

Should always be Self
Source§

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

Source§

type Error = Infallible

The type returned in the event of a conversion error.
Source§

fn try_from(value: U) -> Result<T, <T as TryFrom<U>>::Error>

Performs the conversion.
Source§

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

Source§

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

The type returned in the event of a conversion error.
Source§

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

Performs the conversion.