The Well-Grounded Rubyist, Second Edition

4.2. Modules, classes, and method lookup

You already know that when an object receives a message, the intended (and usual) result is the execution of a method with the same name as the message in the object’s class or that class’s superclass—and onward, up to the Object or even BasicObject class—or in a module that has been mixed into any of those classes. But how does this come about? And what happens in ambiguous cases—for example, if a class and a mixed-in module both define a method with a given name? Which one does the object choose to execute?

It pays to answer these questions precisely. Imprecise accounts of what happens are easy to come by. Sometimes they’re even adequate: if you say, “This object has a push method,” you may succeed in ...