To expand on this: the "unit" here represents the number of possible values that can be returned. The confusion is probably because "empty" can mean two things

To expand on this: the "unit" here represents the number of possible values that can be returned. The confusion is probably because "empty" can mean two things: - What's inside the returned value. That may be why the parent suggested empty for the unit type. But that's now what "unit" means in the common parlance. - How many possible values can be returned. Never returning means the function has zero possible return values.