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Zero-initialize vec![None; n] for Option<&T>, Option<&mut T> and Option<Box<T>> #64893

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Oct 1, 2019
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Zero-initialize vec![None; n] for Option<&T>, Option<&mut T> and Option<Box<T>> #64893

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25 changes: 25 additions & 0 deletions src/liballoc/vec.rs
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Original file line number Diff line number Diff line change
Expand Up @@ -1748,6 +1748,31 @@ unsafe impl<T: ?Sized> IsZero for *mut T {
}
}

// `Option<&T>`, `Option<&mut T>` and `Option<Box<T>>` are guaranteed to represent `None` as null.
// For fat pointers, the bytes that would be the pointer metadata in the `Some` variant
// are padding in the `None` variant, so ignoring them and zero-initializing instead is ok.
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CC #64891


unsafe impl<T: ?Sized> IsZero for Option<&T> {
#[inline]
fn is_zero(&self) -> bool {
self.is_none()
}
}

unsafe impl<T: ?Sized> IsZero for Option<&mut T> {
#[inline]
fn is_zero(&self) -> bool {
self.is_none()
}
}

unsafe impl<T: ?Sized> IsZero for Option<Box<T>> {
#[inline]
fn is_zero(&self) -> bool {
self.is_none()
}
}


////////////////////////////////////////////////////////////////////////////////
// Common trait implementations for Vec
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