Wrap-Up

Here’s a checklist of what you learned today:

• An object is composed of a bunch of instance variables and a link to a class.

• The methods of an object live in the object’s class. (From the point of view of the class, they’re called instance methods.)

• The class itself is just an object of class Class. The name of the class is just a constant.

• Class is a subclass of Module. A module is basically a package of methods. In addition to that, a class can also be instantiated (with new) or arranged in a hierarchy (through its superclass).

• Constants are arranged in a tree similar to a file system, where the names of modules and classes play the part of directories and regular constants play the part of files.

• Each class has an ancestors chain, beginning with the class itself and going up to BasicObject.

• When you call a method, Ruby goes right into the class of the receiver and then up the ancestors chain, until it either finds the method or reaches the end of the chain.

• When you include a module in a class, the module is inserted in the ancestors chain right above the class itself. When you prepend the module, it is inserted in the ancestors chain right below the class.

• When you call a method, the receiver takes the role of self.

• When you’re defining a module (or a class), the module takes the role of self.

• Instance variables are always assumed to be instance variables of self.

• Any method called without an explicit receiver is assumed to be a method of self.

• Refinements are like pieces of code patched right over a class, and they override normal method lookup. On the other hand, a Refinement works in a limited area of the program: the lines of code between the call to using and the end of the file, or the end of the module definition.

Checked…checked…done! Now it’s time to go home before your brain explodes with all the information you crammed into it today.

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