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use crate::cell::Cell;
use crate::fmt;
use crate::ops::Deref;
use crate::panic::{RefUnwindSafe, UnwindSafe};
use crate::sync::OnceLock;
#[unstable(feature = "once_cell", issue = "74465")]
pub struct LazyLock<T, F = fn() -> T> {
cell: OnceLock<T>,
init: Cell<Option<F>>,
}
impl<T, F> LazyLock<T, F> {
#[unstable(feature = "once_cell", issue = "74465")]
pub const fn new(f: F) -> LazyLock<T, F> {
LazyLock { cell: OnceLock::new(), init: Cell::new(Some(f)) }
}
}
impl<T, F: FnOnce() -> T> LazyLock<T, F> {
#[unstable(feature = "once_cell", issue = "74465")]
pub fn force(this: &LazyLock<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 LazyLock<T, F> {
type Target = T;
fn deref(&self) -> &T {
LazyLock::force(self)
}
}
#[unstable(feature = "once_cell", issue = "74465")]
impl<T: Default> Default for LazyLock<T> {
fn default() -> LazyLock<T> {
LazyLock::new(T::default)
}
}
#[unstable(feature = "once_cell", issue = "74465")]
impl<T: fmt::Debug, F> fmt::Debug for LazyLock<T, F> {
fn fmt(&self, f: &mut fmt::Formatter<'_>) -> fmt::Result {
f.debug_struct("Lazy").field("cell", &self.cell).finish_non_exhaustive()
}
}
#[unstable(feature = "once_cell", issue = "74465")]
unsafe impl<T, F: Send> Sync for LazyLock<T, F> where OnceLock<T>: Sync {}
#[unstable(feature = "once_cell", issue = "74465")]
impl<T, F: UnwindSafe> RefUnwindSafe for LazyLock<T, F> where OnceLock<T>: RefUnwindSafe {}
#[unstable(feature = "once_cell", issue = "74465")]
impl<T, F: UnwindSafe> UnwindSafe for LazyLock<T, F> where OnceLock<T>: UnwindSafe {}
#[cfg(test)]
mod tests;