Class Hierarchies

Abstract

There is more to polymorphism than merely abstract data types that can have different concrete implementations. A fundamental concept found in most object-oriented programming languages is classes and class hierarchies. Class hierarchies serve two conceptually different purposes: refinement of object interfaces and code reuse. Neither concept, strictly speaking, requires class hierarchies in R, since R is dynamically typed, unlike programming languages such as C++ or Java where class hierarchies and the static type system are intertwined. Nevertheless, class hierarchies provide a framework for thinking about software design that is immensely useful, not least in dynamically typed languages.