pub fn new_zeroed_slice_in(len: usize, alloc: A) -> Box<[mem::MaybeUninit<T>], A> {
        unsafe { RawVec::with_capacity_zeroed_in(len, alloc).into_box(len) }
    }
Constructs a box from a raw pointer.

After calling this function, the raw pointer is owned by the
resulting `Box`. Specifically, the `Box` destructor will call
the destructor of `T` and free the allocated memory. For this
to be safe, the memory must have been allocated in accordance
with the [memory layout] used by
benchmarks/haystacks/code/rust-library.rs