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Tighten/clarify documentation of rc data_offset

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CAD97 2021-01-07 12:32:42 -05:00
parent 6bc772cdc0
commit f00b458903
2 changed files with 4 additions and 10 deletions
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7
library/alloc/src/rc.rs
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@ -2325,11 +2325,8 @@ impl<T: ?Sized> Unpin for Rc<T> {}
///
/// # Safety
///
/// This has the same safety requirements as `align_of_val_raw`. In effect:
///
/// - This function is safe for any argument if `T` is sized, and
/// - if `T` is unsized, the pointer must have appropriate pointer metadata
/// acquired from the real instance that you are getting this offset for.
/// The pointer must point to (and have valid metadata for) a previously
/// valid instance of T, but the T is allowed to be dropped.
unsafe fn data_offset<T: ?Sized>(ptr: *const T) -> isize {
// Align the unsized value to the end of the `RcBox`.
// Because it is ?Sized, it will always be the last field in memory.

7
library/alloc/src/sync.rs
View File

@ -2476,11 +2476,8 @@ impl<T: ?Sized> Unpin for Arc<T> {}
///
/// # Safety
///
/// This has the same safety requirements as `align_of_val_raw`. In effect:
///
/// - This function is safe for any argument if `T` is sized, and
/// - if `T` is unsized, the pointer must have appropriate pointer metadata
/// acquired from the real instance that you are getting this offset for.
/// The pointer must point to (and have valid metadata for) a previously
/// valid instance of T, but the T is allowed to be dropped.
unsafe fn data_offset<T: ?Sized>(ptr: *const T) -> isize {
// Align the unsized value to the end of the `ArcInner`.
// Because it is `?Sized`, it will always be the last field in memory.