In this chapter, you learn how to add methods to a class in a modular fashion through the use of categories and how to create a standardized list of methods for others to implement.
Sometimes you might be working with a class definition and want to add some new methods to it. For example, you might decide for your
Fraction class that, in addition to the
add: method for adding two fractions, you want to have methods to subtract, multiply, and divide two fractions.
As another example, suppose that you are working on a large programming project and, as part of that project, your group is defining a new class that contains many different methods. You have been assigned the task of writing methods for the class ...