pub struct Lazy<T, F = fn() -> T> { /* private fields */ }
Available on crate feature
macros
only.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>where
F: FnOnce() -> T,
impl<T, F> Lazy<T, F>where
F: FnOnce() -> T,
sourcepub 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);
sourcepub fn force_mut(this: &mut Lazy<T, F>) -> &mut T
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);
sourcepub 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));
sourcepub fn get_mut(this: &mut Lazy<T, F>) -> Option<&mut T>
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§
impl<T, F> RefUnwindSafe for Lazy<T, F>
impl<T, F> Sync for Lazy<T, F>
Auto Trait Implementations§
impl<T, F = fn() -> T> !Freeze for Lazy<T, F>
impl<T, F> Send for Lazy<T, F>
impl<T, F> Unpin for Lazy<T, F>
impl<T, F> UnwindSafe for Lazy<T, F>where
T: UnwindSafe,
F: 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
source§impl<T> Ext for T
impl<T> Ext for T
source§fn assert_normalized(self) -> AssertNormalized<T>
fn assert_normalized(self) -> AssertNormalized<T>
source§fn normalized<W>(self) -> Normalize<W, T>
fn normalized<W>(self) -> Normalize<W, T>
source§fn summarized(self) -> Summarize<T>
fn summarized(self) -> Summarize<T>
source§fn fail_on_skipped(self) -> FailOnSkipped<T>
fn fail_on_skipped(self) -> FailOnSkipped<T>
source§fn fail_on_skipped_with<F>(self, f: F) -> FailOnSkipped<T, F>
fn fail_on_skipped_with<F>(self, f: F) -> FailOnSkipped<T, F>
source§fn repeat_skipped<W>(self) -> Repeat<W, T>
fn repeat_skipped<W>(self) -> Repeat<W, T>
source§fn repeat_failed<W>(self) -> Repeat<W, T>
fn repeat_failed<W>(self) -> Repeat<W, T>
source§fn repeat_if<W, F>(self, filter: F) -> Repeat<W, T, F>
fn repeat_if<W, F>(self, filter: F) -> Repeat<W, T, F>
Wraps this
Writer
to re-output filter
ed events at the end of an
output.source§fn tee<W, Wr>(self, other: Wr) -> Tee<T, Wr>where
Wr: Writer<W>,
fn tee<W, Wr>(self, other: Wr) -> Tee<T, Wr>where
Wr: Writer<W>,
Attaches the provided
other
Writer
to the current one for passing
events to both of them simultaneously.source§fn discard_arbitrary_writes(self) -> Arbitrary<T>
fn discard_arbitrary_writes(self) -> Arbitrary<T>
Wraps this
Writer
into a discard::Arbitrary
one, providing a
no-op ArbitraryWriter
implementation. Read moresource§fn discard_stats_writes(self) -> Stats<T>
fn discard_stats_writes(self) -> Stats<T>
Wraps this
Writer
into a discard::Stats
one, providing a no-op
StatsWriter
implementation returning only 0
. Read moresource§impl<T> Instrument for T
impl<T> Instrument for T
source§fn instrument(self, span: Span) -> Instrumented<Self>
fn instrument(self, span: Span) -> Instrumented<Self>
source§fn in_current_span(self) -> Instrumented<Self>
fn in_current_span(self) -> Instrumented<Self>
source§impl<T> IntoEither for T
impl<T> IntoEither for T
source§fn into_either(self, into_left: bool) -> Either<Self, Self> ⓘ
fn into_either(self, into_left: bool) -> Either<Self, Self> ⓘ
Converts
self
into a Left
variant of Either<Self, Self>
if into_left
is true
.
Converts self
into a Right
variant of Either<Self, Self>
otherwise. Read moresource§fn into_either_with<F>(self, into_left: F) -> Either<Self, Self> ⓘ
fn into_either_with<F>(self, into_left: F) -> Either<Self, Self> ⓘ
Converts
self
into a Left
variant of Either<Self, Self>
if into_left(&self)
returns true
.
Converts self
into a Right
variant of Either<Self, Self>
otherwise. Read more