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use crate::cell::{Cell, OnceCell};
use crate::fmt;
use crate::ops::Deref;
#[unstable(feature = "once_cell", issue = "74465")]
pub struct LazyCell<T, F = fn() -> T> {
cell: OnceCell<T>,
init: Cell<Option<F>>,
}
impl<T, F> LazyCell<T, F> {
#[unstable(feature = "once_cell", issue = "74465")]
pub const fn new(init: F) -> LazyCell<T, F> {
LazyCell { cell: OnceCell::new(), init: Cell::new(Some(init)) }
}
}
impl<T, F: FnOnce() -> T> LazyCell<T, F> {
#[unstable(feature = "once_cell", issue = "74465")]
pub fn force(this: &LazyCell<T, F>) -> &T {
this.cell.get_or_init(|| match this.init.take() {
Some(f) => f(),
None => panic!("`Lazy` instance has previously been poisoned"),
})
}
}
#[unstable(feature = "once_cell", issue = "74465")]
impl<T, F: FnOnce() -> T> Deref for LazyCell<T, F> {
type Target = T;
fn deref(&self) -> &T {
LazyCell::force(self)
}
}
#[unstable(feature = "once_cell", issue = "74465")]
impl<T: Default> Default for LazyCell<T> {
fn default() -> LazyCell<T> {
LazyCell::new(T::default)
}
}
#[unstable(feature = "once_cell", issue = "74465")]
impl<T: fmt::Debug, F> fmt::Debug for LazyCell<T, F> {
fn fmt(&self, f: &mut fmt::Formatter<'_>) -> fmt::Result {
f.debug_struct("Lazy").field("cell", &self.cell).field("init", &"..").finish()
}
}