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Vec drop and truncate: drop using raw slice *mut [T] #71148

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merged 2 commits into from
May 1, 2020
Merged

Vec drop and truncate: drop using raw slice *mut [T] #71148

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Vec drop and truncate: drop using raw slice *mut [T]
bluss Apr 14, 2020
f654daf
Vec IntoIter: Drop using raw slice
bluss Apr 28, 2020
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14 changes: 10 additions & 4 deletions src/liballoc/vec.rs
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Original file line number Diff line number Diff line change
Expand Up @@ -741,7 +741,7 @@ impl<T> Vec<T> {
return;
}
let remaining_len = self.len - len;
let s = slice::from_raw_parts_mut(self.as_mut_ptr().add(len), remaining_len);
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let s = ptr::slice_from_raw_parts_mut(self.as_mut_ptr().add(len), remaining_len);
self.len = len;
ptr::drop_in_place(s);
}
Expand Down Expand Up @@ -2379,7 +2379,9 @@ unsafe impl<#[may_dangle] T> Drop for Vec<T> {
fn drop(&mut self) {
unsafe {
// use drop for [T]
ptr::drop_in_place(&mut self[..]);
// use a raw slice to refer to the elements of the vector as weakest necessary type;
// could avoid questions of validity in certain cases
ptr::drop_in_place(ptr::slice_from_raw_parts_mut(self.as_mut_ptr(), self.len))
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Might be worth adding a brief comment for why we use this complicated operation here instead of the simple one.

Really, already for #70558, what we should really have is a way to get a raw slice for the entire Vec, and then subslicing on raw slices. Then we would not have to call slice_from_raw_parts for any of the methods changed in that PR or here.

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Comment added, though it's very vague since I don't dare say so much about what it actually allows

}
// RawVec handles deallocation
}
Expand Down Expand Up @@ -2596,7 +2598,11 @@ impl<T> IntoIter<T> {
/// ```
#[stable(feature = "vec_into_iter_as_slice", since = "1.15.0")]
pub fn as_mut_slice(&mut self) -> &mut [T] {
unsafe { slice::from_raw_parts_mut(self.ptr as *mut T, self.len()) }
unsafe { &mut *self.as_raw_mut_slice() }
}

fn as_raw_mut_slice(&mut self) -> *mut [T] {
ptr::slice_from_raw_parts_mut(self.ptr as *mut T, self.len())
}
}

Expand Down Expand Up @@ -2708,7 +2714,7 @@ unsafe impl<#[may_dangle] T> Drop for IntoIter<T> {
let guard = DropGuard(self);
// destroy the remaining elements
unsafe {
ptr::drop_in_place(guard.0.as_mut_slice());
ptr::drop_in_place(guard.0.as_raw_mut_slice());
}
// now `guard` will be dropped and do the rest
}
Expand Down