Module

A Module is a collection of methods and constants. The methods in a module may be instance methods or module methods. Instance methods appear as methods in a class when the module is included, module methods do not. Conversely, module methods may be called without creating an encapsulating object, while instance methods may not. (See Module#module_function.)

In the descriptions that follow, the parameter sym refers to a symbol, which is either a quoted string or a Symbol (such as :name).

moduleModincludeMathCONST=1defmeth# ...endendMod.class#=> ModuleMod.constants#=> [:CONST, :PI, :E]Mod.instance_methods#=> [:meth]

Module Reference

Class

Classes in Ruby are first-class objects—each is an instance of class Class.

Typically, you create a new class by using:

className# some code describing the class behaviorend

When a new class is created, an object of type Class is initialized and assigned to a global constant (Name in this case).

When Name.new is called to create a new object, the #new method in Class is run by default. This can be demonstrated by overriding #new in Class:

classClassaliasold_newnewdefnew(*args)print"Creating a new ",self.name,"\n"old_new(*args)endendclassNameendn=Name.new

produces:

CreatinganewName

Classes, modules, and objects are interrelated. In the diagram that follows, the vertical arrows represent inheritance, and the parentheses metaclasses. All metaclasses are instances of the class Class.

 +---------+ +-... | | | BasicObject-----|-->(BasicObject)-------|-... ^ | ^ | | | | | Object---------|----->(Object)---------|-... ^ | ^ | | | | | +-------+ | +--------+ | | | | | | | | Module-|---------|--->(Module)-|-... | ^ | | ^ | | | | | | | | Class-|---------|---->(Class)-|-... | ^ | | ^ | | +---+ | +----+ | | obj--->OtherClass---------->(OtherClass)-----------...

Class Reference

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