Eloquent Ruby (Addison-Wesley Professional Ruby Series)

To understand Ruby programs—both your own and others’—you need to know about Ruby’s notion of a current default object, known by the keyword self.

Inheritance is a kind of downward-chaining relationship between two classes (the superclass and the subclass), whereby one class “inherits” from another, and the instances of the subclass acquire the behaviors—the methods—defined in the superclass.

Again, the logic required to figure out what object owns a given instance variable is simple and consistent: every instance variable belongs to whatever object is playing the role of self at the moment the code containing the instance variable is executed.