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Add a comment for covariant Ref

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This commit is contained in:
Josh Stone 2022-05-16 17:24:53 -07:00
parent 1e53fab55a
commit 1f33c921d1
1 changed files with 2 additions and 1 deletions
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library/core/src/cell.rs
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@ -1318,6 +1318,7 @@ impl Clone for BorrowRef<'_> {
pub struct Ref<'b, T: ?Sized + 'b> {
// NB: we use a pointer instead of `&'b T` to avoid `noalias` violations, because a
// `Ref` argument doesn't hold immutability for its whole scope, only until it drops.
// `NonNull` is also covariant over `T`, just like we would have with `&T`.
value: NonNull<T>,
borrow: BorrowRef<'b>,
}
@ -1704,7 +1705,7 @@ pub struct RefMut<'b, T: ?Sized + 'b> {
// `RefMut` argument doesn't hold exclusivity for its whole scope, only until it drops.
value: NonNull<T>,
borrow: BorrowRefMut<'b>,
// NonNull is covariant over T, so we need to reintroduce invariance.
// `NonNull` is covariant over `T`, so we need to reintroduce invariance.
marker: PhantomData<&'b mut T>,
}