Ruby has, at its root, an Object. Methods available in Object are available to every class because every class in Ruby inherits from Object somewhere in its own class hierarchy. Of course, you can override methods in subclasses, changing the functionality of a root method. You might stumble on to this idea if you work through Test Driven Development By Example by Kent Beck, translating the Java code into Ruby as you go. At some point pretty early on, he overrides the equality method on the Curre...