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| -rw-r--r-- | src/libcore/ptr.rs | 9 |
1 files changed, 9 insertions, 0 deletions
diff --git a/src/libcore/ptr.rs b/src/libcore/ptr.rs index 53d41976030..a3cf8b63483 100644 --- a/src/libcore/ptr.rs +++ b/src/libcore/ptr.rs @@ -2874,6 +2874,15 @@ impl<'a, T: ?Sized> From<NonNull<T>> for Unique<T> { /// Usually this won't be necessary; covariance is correct for most safe abstractions, /// such as Box, Rc, Arc, Vec, and LinkedList. This is the case because they /// provide a public API that follows the normal shared XOR mutable rules of Rust. +/// +/// Notice that `NonNull<T>` has a `From` instance for `&T`. However, this does +/// not change the fact that mutating through a (pointer derived from a) shared +/// reference is undefined behavior unless the mutation happens inside an +/// [`UnsafeCell<T>`]. When using this `From` instance without an `UnsafeCell<T>`, +/// it is your responsibility to ensure that `as_mut` is never called, and `as_ptr` +/// is never used for mutation. +/// +/// [`UnsafeCell<T>`]: ../cell/struct.UnsafeCell.html #[stable(feature = "nonnull", since = "1.25.0")] #[repr(transparent)] #[rustc_layout_scalar_valid_range_start(1)] |