It is often desirable to be able to specify responses to unexpected events. As it turns out, this is most easily done if we can pass blocks of code as arguments to other methods, which means we want to be …

Modules in ruby are similar to classes, except:

• A module can have no instances.
• A module can have no subclasses.
• A module is defined by module ... end

Actually... the Module class of module is the superclass of the Class …

The behavior of an instance is determined by its class, but there may be times we know that a particular instance should have special behavior. In most languages, we must go to the trouble of defining another class, which would …

Earlier, we said that ruby has no functions, only methods. However there is more than one kind of method. In this chapter we introduce access controls .

Consider what happens when we define a method in the "top level", not …

In a subclass, we can change the behavior of the instances by redefining superclass methods.

ruby> class Human
    |   def identify
    |     print "I'm a person.\n"
    |   end
    |   def train_toll(age)
    |     if age < 12
    |       print "Reduced fare.\n"; …

Our classification of objects in everyday life is naturally hierarchical. We know that all cats are mammals , and all mammals are animals . Smaller classes inherit characteristics from the larger classes to which they belong. If all mammals breathe, …

The real world is filled by objects, and we can classify them. For example, a very small child is likely to say "bow-wow" when seeing a dog, regardless of the breed; we naturally see the world in terms of these …

What is a method? In OO programming, we don't think of operating on data directly from outside an object; rather, objects have some understanding of how to operate on themselves (when asked nicely to do so). You might say we …

Object oriented is a catchy phrase. To call anything object oriented can make you sound pretty smart. Ruby claims to be an object oriented scripting language; but what exactly does "object oriented" mean?

There have been a variety of answers …

Iterators are not an original concept with ruby. They are in common use in object-oriented languages. They are also used in Lisp, though there they are not called iterators. However the concepet of iterator is an unfamiliar one for many …