That example bothered me as well mostly because when the move function is placed outside of the class it is now performing a different action. The new function

That example bothered me as well mostly because when the move function is placed outside of the class it is now performing a different action. The new function no longer really moves a point so much as it adds two points (regardless of the point/vector issue). I think many of the naming conventions commonly used in OOP for mutable objects are not as appropriate for their immutable counterparts.