Introduction to OOP: Chapter 10: Subclasses and Subtypes
Binding in Objective-C
Mixed types - both static and dynamic typing depending upon declarations.
Values maintain their own type information
Legality of message passing can be check at run-time
(Can be tested directly by programmers if desired).
Reverse polymorphism is not a problem in dynamically typed languages,
casts provided for converting statically typed values.
Intro OOP, Chapter 10, Slide 16