1. types in Ruby and other languages…

2.  Classes and objects (vs prototypes)  Instance variables/encapsulation  Object creation  Object equality/comparison  Object type type-safety type conversions  Class methods  Class variables  Inheritance – another lecture

3.  Widening Conversions: can include at least approximations to all of the values of the original type. Examples (Java/C++) byte to short, int, long, float or double short to int, long, float or double char to int, long, float or double int to long, float or double long to float or double float to double  Narrowing conversions: cannot include all of the values of the original type short to byte or char char to byte or short int to byte, short, or char long to byte, short, char or int float to byte, short, char, int or long double to byte, short, char, int, long or float

4.  Even widening conversions may lose accuracy. Example: integers stored in 32 bits, 9 digits of precision. Floating point values also stored in 32 bits, only about 7 digits of precision (because of space used for exponent). Conversions should be used with care! Warnings should not just be ignored… Strongly typed language minimizes type conversions

5.  Every value in Ruby is (or behaves like) an object 2.times { puts “hey”}  Objects are instances of classes  BasicObject is superclass  Objects are strictly encapsulated What does that mean? Not covered: frozen or tainted objects

6.  Protect instance variables from outside forces (i.e., other classes)  Ruby is strictly encapsulated – you must include setters/getter  Java provides encapsulation – but is it strictly encapsulated? (hint: what is the purpose of access modifiers)

7.  Every class inherits method new calls allocate to get space (can’t override) calls initialize to create instance variables  Often convenient to provide default parameters for initialize def initialize(x, y, z=nil) @x, @y, @z = x,y,z end

8. class Cat def initialize(name, age) @name, @age = name, age end def to_s "(#@name, #@age)" end def name @name end def age @age end def name=(value) @name=value end def age=(value) @age=value end c = Cat.new("Fluffy", 2) puts c puts c.name c.age=5 puts c.age puts c.to_s new calls initialize to_s like toString getters and setters, called attributes last expression in function is return @ indicates instance variable always refer to self DO NOT declare outside of method

9. class Bottle attr_accessor :ounces attr_reader :label def initialize(label, ounces) @label = label @ounces = ounces end def add(other) Bottle.new(@label, @ounces+other.ounces) end def add!(other) @ounces += other.ounces other.ounces = 0 end def split(scalar) newOunces = @ounces / scalar @ounces -= newOunces Bottle.new(@label, newOunces) end def +(amount) Bottle.new(@label, @ounces + amount) end def to_s # with an accessor, don't need @ - why? "(#{label}, #{ounces})" end b = Bottle.new("Tab", 16) puts b.label b.ounces = 20 puts "b is #{b}“ puts "result of b2 = b.split 4" b2 = b.split 4 puts "b is #{b}" puts "b2 is #{b2}“ puts "result of b3 = b.add(b2)" b3 = b.add(b2) puts "b3 is #{b3}“ puts "result of b.add!(b2)" b.add!(b2) puts "b is #{b}" puts "b2 is #{b2}“ puts "result of b4 = b3 + 10" b4 = b3 + 10 puts "b4 is #{b4}" attr is example of metaprogramming

10.  From wikipedia:  Polymorphism (from the Greek many forms) is the provision of a single interface to entities of different types

11.  If a function denotes different and potentially heterogeneous implementations depending on a limited range of individually specified types and combinations, it is called ad hoc polymorphism. Ad hoc polymorphism is supported in many languages using function overloading.  If the code is written without mention of any specific type and thus can be used transparently with any number of new types, it is called parametric polymorphism. In the object-oriented programming community, this is often known as generics or generic programming. See also: http://stackoverflow.com/questions/154577/polymorphism-vs-overriding-vs-overloading

12. class Can attr_accessor :ounces def initialize(label, ounces) @label = label @ounces = ounces end def to_s "(#@label, #@ounces)" end b = Bottle.new("Tab", 16) c = Can.new(“Coke", 12) b2 = b.add(c) puts "result of b2 = b.add(c)" puts "b2 is #{b2}“ cat = Cat.new b3 = b.add(cat)  If it walks like a duck and quacks like a duck, it must be a duck  any object with needed method will work  undefined method ‘ounces’ for http://beust.com/weblog/2005/04/15/the-perils-of-duck-typing/

13.  x=1  x.instance_of? Fixnum => true  x.instance_of? Numeric => false (even though subclass)  x.is_a? Fixnum => true  x.is_a? Numeric => true  x.is_a? Comparable => true  x.is_a? Object => true  x.class == Fixnum => true  x.class == Numeric => false Quick Ex: how does Java handle?

14.  Class of an object doesn’t change  Type is more fluid… includes set of behaviors (methods it responds to) i.e, Class != Type….whoaaa  respond_to?

15.  equal? checks addresses (like == in Java)  for Object, == is synonym for equal?  Most classes override == (like equal in Java)

16. class Bottle attr_accessor :ounces attr_reader :label def initialize(label, ounces) @label = label @ounces = ounces end def ==(other) return false if ! other.instance_of? Bottle return @ounces == other.ounces && @label == other.label end alias eql? == end # Can also has ounces class Can attr_accessor :ounces def initialize(label, ounces) @label = label @ounces = ounces end b = Bottle.new("Tab", 16) b2 = Bottle.new("Tab", 16) b3 = Bottle.new("Tab", 12) b4 = Bottle.new("Coke", 16) puts "b.equal?(b2) #{b.equal?(b2)}" puts "b == b2 #{b == b2}" puts "b == b3 #{b == b3}" puts "b == b4 #{b == b4}“ puts "b.eql?(b2) #{b.eql?(b2)}" puts "b.eql?(b3) #{b.eql?(b3)}" c = Can.new("Tab", 16) puts "b == c #{b == c}"

17.  Numeric classes will do type conversions when used with==  eql? is like ==, but no type conversion 1.eql? 1.0  can alias eql? with ==  === used with case statement (1..10) === 5 # true, 5 is in range /\d+/ === “123” # true, matches regex String === “s” # true if s is instance of String Other language with eql?/=== feature?

18. class Bottle attr_accessor :ounces attr_reader :label def initialize(label, ounces) @label = label @ounces = ounces end def add(other) raise TypeError, "Bottle argument expected " unless other.is_a? Bottle Bottle.new(@label, @ounces+other.ounces) end def add2(other) raise TypeError, "Bottle argument expected " unless other.respond_to? :ounces Bottle.new(@label, @ounces+other.ounces) end def add3(other) Bottle.new(@label, @ounces+other.ounces) rescue raise TypeError, "Cannot add with an argument that doesn't have ounces" end def to_s "(#@label, #@ounces)" end class Can attr_accessor :ounces def initialize(label, ounces) @label = label @ounces = ounces end def to_s "(#@label, #@ounces)" end class Cat end b = Bottle.new("Tab", 16) c = Can.new("Coke", 12) puts "result of b2 = b.add(c)" b2 = b.add(c) puts "result of b2 = b.add2(c)" b2 = b.add2(c) puts "b2 is #{b2}" puts "result of b2 = b.add3(c)" b2 = b.add3(c) puts "b2 is #{b2}" cat = Cat.new puts "result of b2 = b.add3(cat)" b2 = b.add3(cat)

19. class Bottle attr_accessor :ounces attr_reader :label def initialize(label, ounces) @label = label @ounces = ounces end def each yield @label yield @ounces end def [](index) case index when 0, -2 then @label when 1, -1 then @ounces when :label, "label" then @label when :ounces, "ounces" then @ounces end b = Bottle.new("Tab", 16) puts "using each" b.each {|x| puts x } puts "[ix]" puts b[0] puts b[-2] puts b[1] puts b[-1] puts "[field name]" puts b["label"] puts b[:label] puts b["ounces"] puts b[:ounces]

20.  Implement operator (spaceship)  Like compareTo (-1, 0, 1 and nil if not comparable)  Typically include Comparable module as a mixin  Provides =, >(defined in terms of )  Sometimes write == anyway (e.g., one may be case-sensitive, may be more efficient). Best to be consistent.

21. class Bottle include Comparable attr_accessor :ounces attr_reader :label def initialize(label, ounces) @label = label @ounces = ounces end def hash #based on Effective Java by Bloch code = 17 code = 37 * code + @label.hash code = 37 * code + @ounces.hash code end def (other) return nil unless other.instance_of? Bottle @ounces other.ounces end b = Bottle.new("Tab", 16) b2 = Bottle.new("Tab", 12) b3 = Bottle.new("Coke", 16) b4 = Bottle.new("Tab", 16) puts "b == b2 #{b == b2}" puts "b < b2 #{b < b2}" puts "b > b2 #{b > b2}" puts "b == b3 #{b == b3}" puts "b == b4 #{b == b4}"

22. class Bottle include Comparable attr_accessor :ounces attr_reader :label MAX_OUNCES = 64 @@numBottles = 0 def initialize(label, ounces) @label = label @@numBottles += 1 if ounces > MAX_OUNCES @ounces = MAX_OUNCES else @ounces = ounces end def Bottle.sum(bottles) total = 0 bottles.each {|b| total += b.ounces } total end def to_s "(#@label, #@ounces)" end def self.report #class method puts "Number of bottles created: #@@numBottles" end bottles = Array.new bottles[0] = Bottle.new("Tab", 16) bottles[1] = Bottle.new("Tab", 16) bottles[2] = Bottle.new("Coke", 16) bottles[3] = Bottle.new("Tab", 20) puts "Total ounces: #{Bottle.sum bottles}" b = Bottle.new("Sprite", 72) puts b Bottle.report Not covered: Class Instance Variables

23.  Language Concepts Classes Instance variables Object creation Determine object type Object equality Object comparisons Type conversions Type safety Class methods – next lecture Class variables  Ruby new to_s duck typing

24. Not covered, but may be useful  dup  clone  initialize_copy  marshalling (create from serialized data)