Function from_manuallydrop 

pub unsafe fn from_manuallydrop<T: ?Sized>(
    slot: &mut ManuallyDrop<T>,
) -> OwningRef<'_, T>

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

Safety

Dropping or moving out of the OwningRef leaves the borrowed ManuallyDrop semantically without a value; see ManuallyDrop::drop and ManuallyDrop::take.

You must not use the Box in such a way that would violate the vailidity invariant of the ManuallyDrop<T>.