pub fn new_uninit_slice(len: usize) -> Arc<[mem::MaybeUninit<T>]> {
        unsafe { Arc::from_ptr(Arc::allocate_for_slice(len)) }
    }
Converts to `Arc<[T]>`.

# Safety

As with [`MaybeUninit::assume_init`],
it is up to the caller to guarantee that the inner value
really is in an initialized state.
Calling this when the content is not yet fully initialized
causes immediate undefined behavior.

[`MaybeU
benchmarks/haystacks/code/rust-library.rs