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
sourceimpl<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>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
sourceimpl<T> BorrowMut<T> for Twhere
T: ?Sized,
impl<T> BorrowMut<T> for Twhere
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
sourceimpl<T> Ext for T
impl<T> Ext for T
sourcefn assert_normalized(self) -> AssertNormalized<T>
fn assert_normalized(self) -> AssertNormalized<T>
sourcefn normalized<W>(self) -> Normalize<W, T>
fn normalized<W>(self) -> Normalize<W, T>
sourcefn summarized(self) -> Summarize<T>
fn summarized(self) -> Summarize<T>
sourcefn fail_on_skipped(
self
) -> FailOnSkipped<T, fn(&Feature, Option<&Rule>, &Scenario) -> bool>
fn fail_on_skipped(
self
) -> FailOnSkipped<T, fn(&Feature, Option<&Rule>, &Scenario) -> bool>
sourcefn fail_on_skipped_with<F>(self, f: F) -> FailOnSkipped<T, F>where
F: Fn(&Feature, Option<&Rule>, &Scenario) -> bool,
fn fail_on_skipped_with<F>(self, f: F) -> FailOnSkipped<T, F>where
F: Fn(&Feature, Option<&Rule>, &Scenario) -> bool,
sourcefn repeat_if<W, F>(self, filter: F) -> Repeat<W, T, F>where
F: Fn(&Result<Event<Cucumber<W>>, Error>) -> bool,
fn repeat_if<W, F>(self, filter: F) -> Repeat<W, T, F>where
F: Fn(&Result<Event<Cucumber<W>>, Error>) -> bool,
sourcefn 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 moresourcefn 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 more