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improve the ZST case

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This commit is contained in:
Lokathor 2019-09-21 17:39:37 -06:00
parent 72d3ae2419
commit 55a4eef7b6
1 changed files with 8 additions and 4 deletions
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12
src/allocation.rs
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@ -40,13 +40,17 @@ pub fn try_cast_box<A: Pod, B: Pod>(input: Box<A>) -> Result<Box<B>, (PodCastErr
/// Allocates a `Box<T>` with all of the contents being zeroed out.
///
/// This is not the same as using `Box::new(T::zeroed())`. With this function
/// the contents of the box never exists on the stack, so this can create very
/// large boxes without fear of a stack overflow.
/// This uses the global allocator to create a zeroed allocation and _then_
/// turns it into a Box. In other words, it's 100% assured that the zeroed data
/// won't be put temporarily on the stack. You can make a box of any size
/// without fear of a stack overflow.
///
/// (As a _small_ detail, a zero sized type will box up `T::zeroed()` normally,
/// but since it's zero sized you still can't overflow the stack with it.)
#[inline]
pub fn try_zeroed_box<T: Zeroable>() -> Result<Box<T>, ()> {
if size_of::<T>() == 0 {
return Err(());
return Ok(Box::new(T::zeroed()));
}
let layout = Layout::from_size_align(size_of::<T>(), align_of::<T>()).unwrap();
let ptr = unsafe { alloc_zeroed(layout) };