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use std::cell::Cell;
use std::ptr;
/// Scoped thread-local storage
pub(super) struct Scoped<T> {
pub(super) inner: Cell<*const T>,
}
impl<T> Scoped<T> {
pub(super) const fn new() -> Scoped<T> {
Scoped {
inner: Cell::new(ptr::null()),
}
}
/// Inserts a value into the scoped cell for the duration of the closure
pub(super) fn set<F, R>(&self, t: &T, f: F) -> R
where
F: FnOnce() -> R,
{
struct Reset<'a, T> {
cell: &'a Cell<*const T>,
prev: *const T,
}
impl<T> Drop for Reset<'_, T> {
fn drop(&mut self) {
self.cell.set(self.prev);
}
}
let prev = self.inner.get();
self.inner.set(t as *const _);
let _reset = Reset {
cell: &self.inner,
prev,
};
f()
}
/// Gets the value out of the scoped cell;
pub(super) fn with<F, R>(&self, f: F) -> R
where
F: FnOnce(Option<&T>) -> R,
{
let val = self.inner.get();
if val.is_null() {
f(None)
} else {
unsafe { f(Some(&*val)) }
}
}
}