CSC302 2006S, Class 38: Presentations (2): Objects in Ruby

Admin:
* Presentation by Michael Claveria, Bradley Miller, David Ventresca
* Reading for Friday?
* SamR takes notes in EBoard again.
* Really Late: Alex
* Moral: "Ruby is Awesome"

Overview:
* Classes, How to Use Them
* Inheritance
* Modules and Mixins
* Polymorphism, Overloading, and Other Failures
* Mini Lab

/Class Basics/

* Start with "ruby eval.rb", which starts the Ruby shell
  * Not quite the Ruby shell described in /Beyond Java/, but close enough
* Define classes with the "class" keyword and the name of the class.
  * Class names start with capital letters.
  * Constructors are called "initialize"
  * Fields begin with an at sign
  * Class variables begin with two at signs
* Example
	ruby> class Book
        |   @@numberOfBooks = 0
	    |   def initialize(title, author, contents)
	    |       @title = title
	    |       @author = author
	    |       @contents = contents
        |       @@numberOfBooks = @@numberOfBooks + 1
	    |   end
	    | end
	    nil
	ruby> abook = Book.new("Beyond Java", "O'Reilly", "words")
* You load a file with "require"
  * You can only load once.

/Inheritance/

* Use "<" for subclassing
* The constructor can call the constructor for the superclass with "super"
* Example
    require "book.rb"
    class TextBook < Book
        def initialize(title, author, contents, course)
            super(title, author, contents)
            @course = course
        end
    end
[Good, simple, example]
[I like to see polymorphism here, but later is reasonable.]
* Can override methods
* Method call: Check class, then parent, then grandparent, and so on and so forth
* Ruby shell allows live redefinition of classes

/Modules and Mixins/

* Modules permit you to group related things together.
* Use keyword "module"
* Module names start with capital letters" (it seems)
module Characteristics
  def Characteristics.sex chromosomes
    if chromosomes == 'XY'
       puts 'male'
    elsif chromosomes == 'XX'
       puts 'female'
    else
       puts 'ambiguous'
    end
  end
end

module Drunk_Student
  def Drunk_Student.sex beers
    if beers >= 5
      puts "Too drunk to make a rational decision.  No sex."
    else
      puts "Went to Harris and hooked up."
    end
  end
end

Although both have a sex method, the methods are independent
(and, in fact, have a different name.)

[Difference between modules and classes?  Modules group static
methods]

/Mixins/

Classes can "include" other classes and, by default, get the
methods of those classes

	module Debug
	  def identify
	    "#{self.class} (\##{self.object_id})"
	  end
	end
	
	class Pikachu
	  include Debug
	end
	
	class Jigglypuff
	  include Debug
	end

[Good question from Davis: Why do this instead of subclassing?
Answer: Gets around problems of multiple inheritance.]

[Revised question from Davis: If they inherit a method and
include a method, which wins?]

[Not a lot of discussion]	

/Polymorphism/

class PowerDrill
  def drill
    # drill like a power drill
  end
end

class HandDrill
  def drill
    # drill like a hand drill
  end
end

def goDrill(tool)
  tool.drill
end

We can call goDrill(PowerDrill.new())
We can also call goDrill(HandDrill.new())

No overloading permitted (no two methods with the same name)

/Exercise/

Lab: Shuffle a deck of cards in Ruby

[Sam calls this "permuting" because shuffling works differently]

Part 0: Overview.
        A standard deck of cards has 52! possible permutations. In order to shuffle a deck of cards it is necessary to supply an algorithm that presents an equal chance for any of the permutations to occur.

Part 1: Precoding.
        Discuss possible solutions to the problem.  There is a linear time solution!

Part 2: Deck.
        Create an array of length 52, you can use any naming convention for the
cards, or it can be simply the numbers from 1 to 52, or 0 to 51.

Part 3: Shuffle.
        Write a function that provides the shell of your algorithm.  This 'shell' should simply step through the array and then call a function to perform the required swapping your algorithm requires.

        Write a function swap which performs the linear time algorithm given a position in the array.

Part 4: Test.
        Execute the deck.Shuffle function 10-15 times, or until you are satisfied with your results and print the results of 5 consecutive shuffles.


[Solution given is not guaranteed to be uniform, but is acceptable.]