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Make pointer::with_metadata_of const (+simplify implementation)

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This commit is contained in:
Maybe Waffle 2022-10-28 23:05:22 +04:00
parent 44fcfb0a96
commit 6c54745784
2 changed files with 6 additions and 20 deletions
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11
library/core/src/ptr/const_ptr.rs
View file

@ -79,19 +79,14 @@ impl<T: ?Sized> *const T {
/// }
/// ```
#[unstable(feature = "set_ptr_value", issue = "75091")]
#[rustc_const_unstable(feature = "set_ptr_value", issue = "75091")]
#[must_use = "returns a new pointer rather than modifying its argument"]
#[inline]
pub fn with_metadata_of<U>(self, mut val: *const U) -> *const U
pub const fn with_metadata_of<U>(self, meta: *const U) -> *const U
where
U: ?Sized,
{
let target = &mut val as *mut *const U as *mut *const u8;
// SAFETY: In case of a thin pointer, this operations is identical
// to a simple assignment. In case of a fat pointer, with the current
// fat pointer layout implementation, the first field of such a
// pointer is always the data pointer, which is likewise assigned.
unsafe { *target = self as *const u8 };
val
from_raw_parts::<U>(self as *const (), metadata(meta))
}
/// Changes constness without changing the type.

15
library/core/src/ptr/mut_ptr.rs
View file

@ -78,23 +78,14 @@ impl<T: ?Sized> *mut T {
/// }
/// ```
#[unstable(feature = "set_ptr_value", issue = "75091")]
#[rustc_const_unstable(feature = "set_ptr_value", issue = "75091")]
#[must_use = "returns a new pointer rather than modifying its argument"]
#[inline]
pub fn with_metadata_of<U>(self, val: *const U) -> *mut U
pub const fn with_metadata_of<U>(self, meta: *const U) -> *mut U
where
U: ?Sized,
{
// Prepare in the type system that we will replace the pointer value with a mutable
// pointer, taking the mutable provenance from the `self` pointer.
let mut val = val as *mut U;
// Pointer to the pointer value within the value.
let target = &mut val as *mut *mut U as *mut *mut u8;
// SAFETY: In case of a thin pointer, this operations is identical
// to a simple assignment. In case of a fat pointer, with the current
// fat pointer layout implementation, the first field of such a
// pointer is always the data pointer, which is likewise assigned.
unsafe { *target = self as *mut u8 };
val
from_raw_parts_mut::<U>(self as *mut (), metadata(meta))
}
/// Changes constness without changing the type.