// SPDX-License-Identifier: Apache-2.0 OR MIT 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<T> TrivialDrop for slice::Iter<'_, T> {} impl<T> TrivialDrop for slice::IterMut<'_, T> {} impl<T> TrivialDrop for option::IntoIter<&T> {} impl<T> TrivialDrop for option::IntoIter<&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>>()); }