pub fn new_zeroed_slice(len: usize) -> Box<[mem::MaybeUninit<T>]> {
        unsafe { RawVec::with_capacity_zeroed(len).into_box(len) }
    }
Converts to `Box<T, A>`.

# Safety

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

[`MaybeUninit::assume_init`]: mem::MaybeUninit::assume_init

# Examples

```
#![feature(new_uninit)]

let mut five = Box::<u32>::new_uninit();

let five: Box<u32> = unsafe {
// Deferred initialization:
five.as_mut_ptr().write(5);

five.assume_init()
};

assert_
benchmarks/haystacks/code/rust-library.rs