R Programming By Example

Public methods and polymorphism

To define a method for a class, we need to use the UseMethod() function to define a hierarchy of functions. It will tell R to look for a function whose prefix matches the current function and for a suffix in order from the vector of class names of the object being passed. The names of the methods have two parts, separated by a ".", where the prefix is the function name and the suffix is the name of a class. As you can see, S3 generic functions work by naming conventions, not by explicitly registering methods for different classes.

We start by creating an S3area method for the S3Rectangle class, and we do so by creating a function named S3area.S3Rectangle. The UseMethod() function will make sure that the S3area.S3Rectangle ...