Function copy_into_maybe_uninit_slice 

pub fn copy_into_maybe_uninit_slice<'a, T>(
    src: &[T],
    dst: &'a mut [MaybeUninit<T>],
) -> &'a mut [T]
where
    T: Copy,

Copies the elements from src to dst, returning a mutable reference to the now initialized contents of dst.

If T does not implement Copy, use clone_into_maybe_uninit_slice

This is similar to slice::copy_from_slice. This is identical to the implementation of the method write_to_slice on MaybeUninit, but that API is as yet unstable.

Panics

This function will panic if the two slices have different lengths.