diff options
| -rw-r--r-- | library/alloc/src/vec/mod.rs | 10 |
1 files changed, 7 insertions, 3 deletions
diff --git a/library/alloc/src/vec/mod.rs b/library/alloc/src/vec/mod.rs index 5131168db0c..13d13a9d7d1 100644 --- a/library/alloc/src/vec/mod.rs +++ b/library/alloc/src/vec/mod.rs @@ -479,12 +479,14 @@ impl<T> Vec<T> { /// /// * `ptr` needs to have been previously allocated via [`String`]/`Vec<T>` /// (at least, it's highly likely to be incorrect if it wasn't). - /// * `T` needs to have the same size and alignment as what `ptr` was allocated with. + /// * `T` needs to have the same alignment as what `ptr` was allocated with. /// (`T` having a less strict alignment is not sufficient, the alignment really /// needs to be equal to satisfy the [`dealloc`] requirement that memory must be /// allocated and deallocated with the same layout.) + /// * The size of `T` times the `capacity` (ie. the allocated size in bytes) needs + /// to be the same size as the pointer was allocated with. (Because similar to + /// alignment, [`dealloc`] must be called with the same layout `size`.) /// * `length` needs to be less than or equal to `capacity`. - /// * `capacity` needs to be the capacity that the pointer was allocated with. /// /// Violating these may cause problems like corrupting the allocator's /// internal data structures. For example it is **not** safe @@ -492,7 +494,9 @@ impl<T> Vec<T> { /// It's also not safe to build one from a `Vec<u16>` and its length, because /// the allocator cares about the alignment, and these two types have different /// alignments. The buffer was allocated with alignment 2 (for `u16`), but after - /// turning it into a `Vec<u8>` it'll be deallocated with alignment 1. + /// turning it into a `Vec<u8>` it'll be deallocated with alignment 1. To avoid + /// these issues, it is often preferable to do casting/transmuting using + /// [`slice::from_raw_parts`] instead. /// /// The ownership of `ptr` is effectively transferred to the /// `Vec<T>` which may then deallocate, reallocate or change the |