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Make Vec::split_at_spare_mut impl safer & simplier

This commit is contained in:
Waffle 2021-03-03 01:04:20 +03:00
parent 9c4e3af39d
commit a1835bcb01
1 changed files with 5 additions and 9 deletions
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14
library/alloc/src/vec/mod.rs
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@ -1944,20 +1944,16 @@ impl<T, A: Allocator> Vec<T, A> {
#[unstable(feature = "vec_split_at_spare", issue = "81944")]
#[inline]
pub fn split_at_spare_mut(&mut self) -> (&mut [T], &mut [MaybeUninit<T>]) {
let ptr = self.as_mut_ptr();
// SAFETY:
// - `ptr` is guaranteed to be in bounds for `capacity` elements
// - `len` is guaranteed to less or equal to `capacity`
// - `MaybeUninit<T>` has the same layout as `T`
let spare_ptr = unsafe { ptr.cast::<MaybeUninit<T>>().add(self.len) };
let Range { start: ptr, end: spare_ptr } = self.as_mut_ptr_range();
let spare_ptr = spare_ptr.cast::<MaybeUninit<T>>();
let spare_len = self.buf.capacity() - self.len;
// SAFETY:
// - `ptr` is guaranteed to be valid for `len` elements
// - `spare_ptr` is offseted from `ptr` by `len`, so it doesn't overlap `initialized` slice
// - `spare_ptr` is pointing one element past the buffer, so it doesn't overlap with `initialized` slice
unsafe {
let initialized = slice::from_raw_parts_mut(ptr, self.len);
let spare = slice::from_raw_parts_mut(spare_ptr, self.buf.capacity() - self.len);
let spare = slice::from_raw_parts_mut(spare_ptr, spare_len);
(initialized, spare)
}