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Document the lifetime requirement of byte_offset and byte_add (#12893)

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# Objective

`byte_offset` and `byte_add` of `Ptr`, `PtrMut` and `OwningPtr` are
missing the lifetime requirement.

## Solution

Add documents.
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orzogc 2024-04-09 01:13:35 +08:00 committed by GitHub
parent c0aa5170bc
commit 5570315baf
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2 changed files with 11 additions and 3 deletions
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12
crates/bevy_ecs/src/storage/blob_vec.rs
View file

@ -310,8 +310,11 @@ impl BlobVec {
// - `new_len` is less than the old len, so it must fit in this vector's allocation.
// - `size` is a multiple of the erased type's alignment,
// so adding a multiple of `size` will preserve alignment.
// - The removed element lives as long as this vector's mutable reference.
let p = unsafe { self.get_ptr_mut().byte_add(new_len * size) };
p.promote()
// SAFETY: The removed element is unreachable by this vector so it's safe to promote the
// `PtrMut` to an `OwningPtr`.
unsafe { p.promote() }
}
/// Removes the value at `index` and copies the value stored into `ptr`.
@ -364,7 +367,8 @@ impl BlobVec {
// - The caller ensures that `index` fits in this vector,
// so this operation will not overflow the original allocation.
// - `size` is a multiple of the erased type's alignment,
// so adding a multiple of `size` will preserve alignment.
// so adding a multiple of `size` will preserve alignment.
// - The element at `index` outlives this vector's reference.
unsafe { self.get_ptr().byte_add(index * size) }
}
@ -380,7 +384,8 @@ impl BlobVec {
// - The caller ensures that `index` fits in this vector,
// so this operation will not overflow the original allocation.
// - `size` is a multiple of the erased type's alignment,
// so adding a multiple of `size` will preserve alignment.
// so adding a multiple of `size` will preserve alignment.
// - The element at `index` outlives this vector's mutable reference.
unsafe { self.get_ptr_mut().byte_add(index * size) }
}
@ -422,6 +427,7 @@ impl BlobVec {
// * 0 <= `i` < `len`, so `i * size` must be in bounds for the allocation.
// * `size` is a multiple of the erased type's alignment,
// so adding a multiple of `size` will preserve alignment.
// * The item lives until it's dropped.
// * The item is left unreachable so it can be safely promoted to an `OwningPtr`.
// NOTE: `self.get_unchecked_mut(i)` cannot be used here, since the `debug_assert`
// would panic due to `self.len` being set to 0.

2
crates/bevy_ptr/src/lib.rs
View file

@ -217,6 +217,7 @@ macro_rules! impl_ptr {
/// - The offset cannot make the existing ptr null, or take it out of bounds for its allocation.
/// - If the `A` type parameter is [`Aligned`] then the offset must not make the resulting pointer
/// be unaligned for the pointee type.
/// - The value pointed by the resulting pointer must outlive the lifetime of this pointer.
///
/// [ptr_offset]: https://doc.rust-lang.org/std/primitive.pointer.html#method.offset
#[inline]
@ -238,6 +239,7 @@ macro_rules! impl_ptr {
/// - The offset cannot make the existing ptr null, or take it out of bounds for its allocation.
/// - If the `A` type parameter is [`Aligned`] then the offset must not make the resulting pointer
/// be unaligned for the pointee type.
/// - The value pointed by the resulting pointer must outlive the lifetime of this pointer.
///
/// [ptr_add]: https://doc.rust-lang.org/std/primitive.pointer.html#method.add
#[inline]