Function from_maybeuninit 

pub unsafe fn from_maybeuninit<T>(slot: &mut MaybeUninit<T>) -> OwningRef<'_, T>

Create a OwningRef<'a, T> from a &'a mut MaybeUninit<T>>.

Safety

The T must be initialized, see MaybeUninit::assume_init_mut and MaybeUninit::assume_init_drop.