| 1 | |
| 2 |
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| 3 | use std::iter;
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| 4 | use std::mem::ManuallyDrop;
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| 5 | use std::ops::{Deref, DerefMut};
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| 6 | use std::option;
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| 7 | use std::slice;
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| 8 |
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| 9 | #[repr(transparent)]
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| 10 | pub(crate) struct NoDrop<T: ?Sized>(ManuallyDrop<T>);
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| 11 |
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| 12 | impl<T> NoDrop<T> {
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| 13 | pub(crate) fn new(value: T) -> Self
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| 14 | where
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| 15 | T: TrivialDrop,
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| 16 | {
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| 17 | NoDrop(ManuallyDrop::new(value))
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| 18 | }
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| 19 | }
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| 20 |
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| 21 | impl<T: ?Sized> Deref for NoDrop<T> {
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| 22 | type Target = T;
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| 23 | fn deref(&self) -> &Self::Target {
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| 24 | &self.0
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| 25 | }
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| 26 | }
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| 27 |
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| 28 | impl<T: ?Sized> DerefMut for NoDrop<T> {
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| 29 | fn deref_mut(&mut self) -> &mut Self::Target {
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| 30 | &mut self.0
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| 31 | }
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| 32 | }
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| 33 |
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| 34 | pub(crate) trait TrivialDrop {}
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| 35 |
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| 36 | impl<T> TrivialDrop for iter::Empty<T> {}
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| 37 | impl<T> TrivialDrop for slice::Iter<'_, T> {}
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| 38 | impl<T> TrivialDrop for slice::IterMut<'_, T> {}
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| 39 | impl<T> TrivialDrop for option::IntoIter<&T> {}
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| 40 | impl<T> TrivialDrop for option::IntoIter<&mut T> {}
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| 41 |
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| 42 | #[test]
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| 43 | fn test_needs_drop() {
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| 44 | use std::mem::needs_drop;
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| 45 |
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| 46 | struct NeedsDrop;
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| 47 |
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| 48 | impl Drop for NeedsDrop {
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| 49 | fn drop(&mut self) {}
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| 50 | }
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| 51 |
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| 52 | assert!(needs_drop::<NeedsDrop>());
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| 53 |
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| 54 | |
| 55 | assert!(!needs_drop::<iter::Empty<NeedsDrop>>());
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| 56 | assert!(!needs_drop::<slice::Iter<NeedsDrop>>());
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| 57 | assert!(!needs_drop::<slice::IterMut<NeedsDrop>>());
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| 58 | assert!(!needs_drop::<option::IntoIter<&NeedsDrop>>());
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| 59 | assert!(!needs_drop::<option::IntoIter<&mut NeedsDrop>>());
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| 60 | }
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