pub struct LazyCell<T, F = fn() -> T> { /* private fields */ }
Expand description
A value which is initialized on the first access.
For a thread-safe version of this struct, see std::sync::LazyLock
.
§Examples
use std::cell::LazyCell;
let lazy: LazyCell<i32> = LazyCell::new(|| {
println!("initializing");
92
});
println!("ready");
println!("{}", *lazy);
println!("{}", *lazy);
// Prints:
// ready
// initializing
// 92
// 92
Implementations§
source§impl<T, F> LazyCell<T, F>where
F: FnOnce() -> T,
impl<T, F> LazyCell<T, F>where
F: FnOnce() -> T,
1.80.0 (const: 1.80.0) · sourcepub const fn new(f: F) -> LazyCell<T, F>
pub const fn new(f: F) -> LazyCell<T, F>
Creates a new lazy value with the given initializing function.
§Examples
use std::cell::LazyCell;
let hello = "Hello, World!".to_string();
let lazy = LazyCell::new(|| hello.to_uppercase());
assert_eq!(&*lazy, "HELLO, WORLD!");
sourcepub const fn into_inner(this: LazyCell<T, F>) -> Result<T, F>
🔬This is a nightly-only experimental API. (lazy_cell_into_inner
)
pub const fn into_inner(this: LazyCell<T, F>) -> Result<T, F>
lazy_cell_into_inner
)Consumes this LazyCell
returning the stored value.
Returns Ok(value)
if Lazy
is initialized and Err(f)
otherwise.
§Examples
#![feature(lazy_cell_into_inner)]
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()));
1.80.0 · sourcepub fn force(this: &LazyCell<T, F>) -> &T
pub fn force(this: &LazyCell<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.
§Examples
use std::cell::LazyCell;
let lazy = LazyCell::new(|| 92);
assert_eq!(LazyCell::force(&lazy), &92);
assert_eq!(&*lazy, &92);
sourcepub fn force_mut(this: &mut LazyCell<T, F>) -> &mut T
🔬This is a nightly-only experimental API. (lazy_get
)
pub fn force_mut(this: &mut LazyCell<T, F>) -> &mut T
lazy_get
)Forces the evaluation of this lazy value and returns a mutable reference to the result.
§Examples
#![feature(lazy_get)]
use std::cell::LazyCell;
let mut lazy = LazyCell::new(|| 92);
let p = LazyCell::force_mut(&mut lazy);
assert_eq!(*p, 92);
*p = 44;
assert_eq!(*lazy, 44);
source§impl<T, F> LazyCell<T, F>
impl<T, F> LazyCell<T, F>
sourcepub fn get_mut(this: &mut LazyCell<T, F>) -> Option<&mut T>
🔬This is a nightly-only experimental API. (lazy_get
)
pub fn get_mut(this: &mut LazyCell<T, F>) -> Option<&mut T>
lazy_get
)Returns a reference to the value if initialized, or None
if not.
§Examples
#![feature(lazy_get)]
use std::cell::LazyCell;
let mut lazy = LazyCell::new(|| 92);
assert_eq!(LazyCell::get_mut(&mut lazy), None);
let _ = LazyCell::force(&lazy);
*LazyCell::get_mut(&mut lazy).unwrap() = 44;
assert_eq!(*lazy, 44);
sourcepub fn get(this: &LazyCell<T, F>) -> Option<&T>
🔬This is a nightly-only experimental API. (lazy_get
)
pub fn get(this: &LazyCell<T, F>) -> Option<&T>
lazy_get
)Returns a mutable reference to the value if initialized, or None
if not.
§Examples
#![feature(lazy_get)]
use std::cell::LazyCell;
let lazy = LazyCell::new(|| 92);
assert_eq!(LazyCell::get(&lazy), None);
let _ = LazyCell::force(&lazy);
assert_eq!(LazyCell::get(&lazy), Some(&92));
Trait Implementations§
Auto Trait Implementations§
impl<T, F = fn() -> T> !Freeze for LazyCell<T, F>
impl<T, F = fn() -> T> !RefUnwindSafe for LazyCell<T, F>
impl<T, F> Send for LazyCell<T, F>
impl<T, F = fn() -> T> !Sync for LazyCell<T, F>
impl<T, F> Unpin for LazyCell<T, F>
impl<T, F> UnwindSafe for LazyCell<T, F>where
F: UnwindSafe,
T: UnwindSafe,
Blanket Implementations§
source§impl<T> BorrowMut<T> for Twhere
T: ?Sized,
impl<T> BorrowMut<T> for Twhere
T: ?Sized,
source§fn borrow_mut(&mut self) -> &mut T
fn borrow_mut(&mut self) -> &mut T
Mutably borrows from an owned value. Read more