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
impl<T, F> Lazy<T, F>
impl<T, F> Lazy<T, F>
pub fn into_value(this: Lazy<T, F>) -> Result<T, F>
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.
impl<T, F> Lazy<T, F> where
F: FnOnce() -> T,
impl<T, F> Lazy<T, F> where
F: FnOnce() -> T,
pub fn force(this: &Lazy<T, F>) -> &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::sync::Lazy;
let lazy = Lazy::new(|| 92);
assert_eq!(Lazy::force(&lazy), &92);
assert_eq!(&*lazy, &92);
pub fn get(this: &Lazy<T, F>) -> Option<&T>
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));
Trait Implementations
impl<T, F> RefUnwindSafe for Lazy<T, F> where
F: RefUnwindSafe,
OnceCell<T>: RefUnwindSafe,
impl<T, F> Sync for Lazy<T, F> where
F: Send,
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
impl<T> ArchivePointee for T
impl<T> ArchivePointee for T
type ArchivedMetadata = ()
type ArchivedMetadata = ()
The archived version of the pointer metadata for this type.
fn pointer_metadata(
&<T as ArchivePointee>::ArchivedMetadata
) -> <T as Pointee>::Metadata
fn pointer_metadata(
&<T as ArchivePointee>::ArchivedMetadata
) -> <T as Pointee>::Metadata
Converts some archived metadata to the pointer metadata for itself.
sourceimpl<T> BorrowMut<T> for T where
T: ?Sized,
impl<T> BorrowMut<T> for T where
T: ?Sized,
const: unstable · sourcefn borrow_mut(&mut self) -> &mut T
fn borrow_mut(&mut self) -> &mut T
Mutably borrows from an owned value. Read more
impl<F, W, T, D> Deserialize<With<T, W>, D> for F where
W: DeserializeWith<F, T, D>,
D: Fallible + ?Sized,
F: ?Sized,
impl<F, W, T, D> Deserialize<With<T, W>, D> for F where
W: DeserializeWith<F, T, D>,
D: Fallible + ?Sized,
F: ?Sized,
fn deserialize(
&self,
deserializer: &mut D
) -> Result<With<T, W>, <D as Fallible>::Error>
fn deserialize(
&self,
deserializer: &mut D
) -> Result<With<T, W>, <D as Fallible>::Error>
Deserializes using the given deserializer
sourceimpl<T> Instrument for T
impl<T> Instrument for T
sourcefn instrument(self, span: Span) -> Instrumented<Self>
fn instrument(self, span: Span) -> Instrumented<Self>
sourcefn in_current_span(self) -> Instrumented<Self>
fn in_current_span(self) -> Instrumented<Self>
sourceimpl<T> WithSubscriber for T
impl<T> WithSubscriber for T
sourcefn with_subscriber<S>(self, subscriber: S) -> WithDispatch<Self> where
S: Into<Dispatch>,
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
sourcefn with_current_subscriber(self) -> WithDispatch<Self>
fn with_current_subscriber(self) -> WithDispatch<Self>
Attaches the current default Subscriber
to this type, returning a
WithDispatch
wrapper. Read more