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use std::iter;
use std::mem::ManuallyDrop;
use std::ops::{Deref, DerefMut};
use std::option;
use std::slice;
#[repr(transparent)]
pub(crate) struct NoDrop<T: ?Sized>(ManuallyDrop<T>);
impl<T> NoDrop<T> {
pub(crate) fn new(value: T) -> Self
where
T: TrivialDrop,
{
NoDrop(ManuallyDrop::new(value))
}
}
impl<T: ?Sized> Deref for NoDrop<T> {
type Target = T;
fn deref(&self) -> &Self::Target {
&self.0
}
}
impl<T: ?Sized> DerefMut for NoDrop<T> {
fn deref_mut(&mut self) -> &mut Self::Target {
&mut self.0
}
}
pub(crate) trait TrivialDrop {}
impl<T> TrivialDrop for iter::Empty<T> {}
impl<'a, T> TrivialDrop for slice::Iter<'a, T> {}
impl<'a, T> TrivialDrop for slice::IterMut<'a, T> {}
impl<'a, T> TrivialDrop for option::IntoIter<&'a T> {}
impl<'a, T> TrivialDrop for option::IntoIter<&'a mut T> {}
#[test]
fn test_needs_drop() {
use std::mem::needs_drop;
struct NeedsDrop;
impl Drop for NeedsDrop {
fn drop(&mut self) {}
}
assert!(needs_drop::<NeedsDrop>());
// Test each of the types with a handwritten TrivialDrop impl above.
assert!(!needs_drop::<iter::Empty<NeedsDrop>>());
assert!(!needs_drop::<slice::Iter<NeedsDrop>>());
assert!(!needs_drop::<slice::IterMut<NeedsDrop>>());
assert!(!needs_drop::<option::IntoIter<&NeedsDrop>>());
assert!(!needs_drop::<option::IntoIter<&mut NeedsDrop>>());
}
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