Learn Ruby 2011 - Session 4 - Objects, Oh My!
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The document covers an educational session on Ruby programming, focusing on object-oriented concepts such as classes, attributes, inheritance, access control, and modules. It illustrates these concepts with code examples, particularly using a 'bookinstock' class and its variations. The session also includes guidance on exercises and readings for further learning in Ruby.
Learn Ruby 2011 - Session 4 - Objects, Oh My!
- 1. Learn Ruby 2011 Session 4
- 2. Our Sponsors Flatsourcing, iSeatz, Koda, and Launchpad
- 3. Objects, Oh My Objects, Attributes, Inheritance & More
- 4. Questions Having any problems? Discover anything cool?
- 5. Classes • Classes are the blueprints of Objects • Classes define the way an Object keeps state, what it’s value is • Classes define the way an Object behaves, what methods it provides
- 6. Classes & Attributes class BookInStock def initialize(isbn, price) @isbn = isbn @price = Float(price) end end
- 7. Classes & Attributes book = BookInStock.new(“1234”, 3.00) p book #<BookInStock:... @isbn=”1234”, @price=3.00>
- 8. Classes & Attributes class BookInStock def initialize(isbn, price) @isbn = isbn @price = Float(price) end def to_s “ISBN: #{@isbn}, price: #{@price}” end end
- 9. Classes & Attributes book = BookInStock.new(“1234”, 3.00) puts book ISBN: 1234, price: 3.00
- 10. Classes & Attributes class BookInStock attr_reader :isbn, :price def initialize(isbn, price) @isbn = isbn @price = Float(price) end end
- 11. Classes & Attributes book = BookInStock.new(“1234”, 3.00) puts “ISBN: #{book.isbn}, price: #{book.price}” ISBN: 1234, price: 3.00
- 12. Classes & Attributes class BookInStock attr_reader :isbn attr_accessor :price def initialize(isbn, price) @isbn = isbn @price = Float(price) end end
- 13. Classes & Attributes book = BookInStock.new(“1234”, 3.00) puts “ISBN: #{book.isbn}, price: #{book.price}” ISBN: 1234, price: 3.00 book.price = 4.00 puts “ISBN: #{book.isbn}, price: #{book.price}” ISBN: 1234, price: 4.00
- 14. Classes & Attributes class BookInStock attr_reader :isbn #attr_accessor :price attr_reader :price attr_writer :price def initialize(isbn, price) @isbn = isbn @price = Float(price) end end
- 15. Classes & Attributes class BookInStock attr_reader :isbn, :price def initialize(isbn, price) @isbn = isbn @price = Float(price) end def price=(new_price) @price = Float(new_price) end end
- 16. Classes & Attributes class BookInStock def initialize(isbn, price) #... @@count += 1 end #... def self.count @@count end end
- 17. Classes & Attributes book1 = BookInStock.new(“1234”, 3.00) puts BookInStock.count 1 book2 = BookInStock.new(“1235”, 5.19) book3 = BookInStock.new(“1236”, 4.00) puts BookInStock.count 3
- 18. Access Control • Public methods (the default) can be called by anyone in any context • Protected methods can only be called by the Class that defines them or its Subclasses • Private methods can only be called by the within the Class that defines them
- 19. Access Control class BookInStock #... private #... protected #... public #... end
- 20. Access Control class BookInStock #... private :method1 protected :method2, :method3 public :method4 end
- 21. Inheritance • Inheritance allows a Subclass to inherit the behavior of it’s parent Class • Ruby is a single-inheritance language
- 22. Inheritance class BookOnSale < BookInStock end book = BookOnSale.new(“12349”, 1.00) puts book puts book.class ISBN: 12349, price: 1.00 BookOnSale
- 23. Modules • Modules provide an additional means of encapsulation • Modules facilitate Mixins.
- 24. Modules module Trig PI = 3.141592654 def Trig.sin(x) #... end def Trig.cos(x) #... end end y = Trig.sin(Trig::PI/4)
- 25. Mixins • Mixins overcome the limitations of single- inheritance • Mixins allow behavior to be added to a class within requiring inheritance
- 26. Mixins module OnSale def on_sale? true end end class BookOnSale < BookInStock include OnSale end b = BookOnSale.new(“12340”, 1.00) puts “Price $#{b.price}!” unless b.on_sale? puts “ONLY $#{b.price}!” if b.on_sale? ONLY $1.00!
- 27. Reviewing • Classes & Attributes • Access Control • Inheritance • Modules • Mixins
- 28. For Next Week For the New to Programming • Read Chapters 9, 10, 11, 12 & 13 in LtP • Complete exercises for each chapter For Everyone • Read Chapter 3, 4, 5 & 6 in PR1.9 • Work through Ruby Koans: about_classes, about_open_classes, about_inheritance, about_modules
- 29. Next Week • More about Blocks and Iterators • Handling Errors
- 30. Exercises • Work on specific Ruby Koans: • ruby about_classes.rb • ruby about_open_classes.rb • ruby about_inheritance.rb • ruby about_modules.rb