Ruby classes & Modules

--sowjanya Mudunuri

References

• The Ruby Programming Language by David Flanagan and Yukihiro Matsumoto

• Beginning Ruby by Peter Cooper

• Disclaimer: This notes is composed from the above referenced books. This presentation is used to help fellow friends who are trying to learn ruby.

Nested Classes• In Ruby its possible to define classes within other classes

• Nested classes are useful when a class depends on other classes but those classes aren’t useful anywhere else

class Calculator

def give_me_sum

Sum.newend

class Sum

end

class Difference

end

end

• Calculator::Sum.new

Modules

• Modules provide a structure to collect Ruby classes, methods and constant into a single, separately named and defined unit

• Useful to avoid clashes with existing classes methods and constants

• It helps to add the functionality of modules into your classes

Namespacing using Modules

• With two files of the same name or two methods of the same name sure will have coding disasters with unexpected functionality

• Modules help solve it by providing namespaces that can contain any number of classes , methods, and constants and allow you to address them directly

Example of Method in a Module

module Conference

def Conference.register

puts “I registered to a conference”

end

end

module Class

def Class.register

puts “I registered to a class”

end

end

Conference.register

Class.register

Info about Modules in Ruby

• You cannot define instances of a module since they are not classes nor they can inherit from anything

• They just provide ways to organize methods, classes, and constants into separate namespaces

Example of two classes with same name

module Admin

class Reporter

attr_accessor :name

end

end

module Customer

class Reporter

attr_accessor :name

end

end

a = Admin::Reporter.new

a.name

d = Customer::Reporter.new

d.name

Modules as Mix-ins• If you want to share some functionality between disparate classes you

can put those methods in a module and include that module into your class

• include takes a module and includes its contents into the current scope

module UsefulStuff

def class_name

self.class.to_s

end

end

class Ticket

include UsefulStuff

end

class Country

include UsefulStuff

end

u = Ticket.new

u.class_name

More on Modules

• Ruby comes with several modules by standard say “Kernel”

• “Kernel” module is included by the class Object

• Examples of Methods of “Kernel” module are puts, print, rand, chop, chomp. Find more about it

http://www.ruby-doc.org/core-2.1.0/Kernel.html

• Ruby also has “Enumerable” and “Comparable” modules which you can include in your classes

Exercise Time!!

• Go to IRB or http://rubyfiddle.com/

• Create a Module named ‘Pasta’ and define a method named ‘prepare’ in it and call the method on the Module

• Create another Module named ‘Vacation’ and define a method named ‘prepare’ in it and call the method on the Module

Exercise Time!!

• Create a Module named ‘GenericMethods’ and define a method named ‘my_class’. The method should return the name of the class. Define another method named ‘decorate’ and the method should print ‘&&&&&&&&&&’

• Now create a class named ‘Cake’ and include the module GenericMethods

• Now play in IRB or rubyfiddle how to call the methods ‘my_class’ and ‘decorate’ from ‘Cake’

Exercise Time!!

• Create a Module named ‘Chess’ and define a class named ‘Player’ and have an attribute named ‘name’

• Create a Module named ‘Sudoku’ and define a class named ‘Player’ and have an attribute named ‘name’

• Go to IRB/rubyfiddle and instantiate the ‘Player’ from Chess and Sudoku