Linux kernel mirror (for testing)
git.kernel.org/pub/scm/linux/kernel/git/torvalds/linux.git
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linux
1// SPDX-License-Identifier: Apache-2.0 OR MIT
2
3use std::iter;
4use std::mem::ManuallyDrop;
5use std::ops::{Deref, DerefMut};
6use std::option;
7use std::slice;
8
9#[repr(transparent)]
10pub(crate) struct NoDrop<T: ?Sized>(ManuallyDrop<T>);
11
12impl<T> NoDrop<T> {
13 pub(crate) fn new(value: T) -> Self
14 where
15 T: TrivialDrop,
16 {
17 NoDrop(ManuallyDrop::new(value))
18 }
19}
20
21impl<T: ?Sized> Deref for NoDrop<T> {
22 type Target = T;
23 fn deref(&self) -> &Self::Target {
24 &self.0
25 }
26}
27
28impl<T: ?Sized> DerefMut for NoDrop<T> {
29 fn deref_mut(&mut self) -> &mut Self::Target {
30 &mut self.0
31 }
32}
33
34pub(crate) trait TrivialDrop {}
35
36impl<T> TrivialDrop for iter::Empty<T> {}
37impl<T> TrivialDrop for slice::Iter<'_, T> {}
38impl<T> TrivialDrop for slice::IterMut<'_, T> {}
39impl<T> TrivialDrop for option::IntoIter<&T> {}
40impl<T> TrivialDrop for option::IntoIter<&mut T> {}
41
42#[test]
43fn test_needs_drop() {
44 use std::mem::needs_drop;
45
46 struct NeedsDrop;
47
48 impl Drop for NeedsDrop {
49 fn drop(&mut self) {}
50 }
51
52 assert!(needs_drop::<NeedsDrop>());
53
54 // Test each of the types with a handwritten TrivialDrop impl above.
55 assert!(!needs_drop::<iter::Empty<NeedsDrop>>());
56 assert!(!needs_drop::<slice::Iter<NeedsDrop>>());
57 assert!(!needs_drop::<slice::IterMut<NeedsDrop>>());
58 assert!(!needs_drop::<option::IntoIter<&NeedsDrop>>());
59 assert!(!needs_drop::<option::IntoIter<&mut NeedsDrop>>());
60}