Thinking in Objects RubyConf 2012

This talk presents OOP fundamentals, and a basic vocabulary that helps to think about programming in OOP languages.

Transcript

1. Thinking
   in
   Objects
   

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2. @joshsusser
   CTO - Cognitive Health Innovations
   RubyRogues
   GoGaRuCo
   

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4. Perspective is worth
   80 I.Q. points.
   –Alan Kay
   

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6. http://www.flickr.com/photos/xlibber/2962488972
   

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7. Object = Identity
   + Behavior
   + State
   OOP = Objects
   + Encapsulation
   + Polymorphism
   + Inheritance
   

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8. It’s all about
   MESSAGES
   

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10. Smalltalk
    (OOP)
    LISP
    (FP) Perl
    (scripting)
    

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11. Object = Identity
    + Behavior
    + State
    

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12. Identity
    $ nslookup github.com
    207.97.227.239
    

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13. Identity
    s = "foo"
    s.object_id #=> 123450
    t = "foo" #=> "foo"
    t.object_id #=> 123780
    

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14. Identity
    s = "foo"; t = "foo"
    s == t #=> true
    s.equal?(t) #=> false
    

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15. Identity
    s = "foo"; t = "foo"
    s << "d" #=> "food"
    t #=> "foo"
    

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16. Behavior
    "foo".methods
    #=> [:<=>, :==, :===, :eql?, :hash,
    :casecmp, :+, :*, :%, :[], :[]=, :insert,
    :length, :size, :bytesize, :empty?,
    :=~, :match, :succ, :succ!, :next,
    :next!, :upto, :index, :reverse, ...]
    

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17. methods
    def even?
    self % 2 == 0
    end
    def odd?
    !self.even?
    end
    

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18. Object = Identity
    + Behavior
    + State
    

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19. uniques
    nil
    true, false
    :ruby, :rails
    

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20. uniques
    GUEST = Object.new
    def GUEST.name
    "Guest User"
    end
    

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21. State
    s = "foo"
    s << "d" #=> "food"
    s.length #=> 4
    

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22. State
    = Behavior
    

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23. Uniform Access
    attr_accessor :first_name
    

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24. Uniform Access
    def first_name
    @first_name
    end
    

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25. Uniform Access
    def first_name
    @full_name.split(" ").first
    end
    

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26. JavaScript
    user.firstName
    user.firstName()
    

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27. GET /index
    •WEB_ROOT/index.html
    •app/views/home/index.erb
    •memcached / varnish
    

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28. Encapsulation
    

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29. Polymorphism
    Duck-typing
    Protocol
    API
    

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30. Object-based
    Objects
    + Encapsulation
    + Polymorphism
    dynamic binding
    

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31. Inheritance
    • Implementation
    • Type
    

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32. Delegation
    • Composition
    - Forwardable
    • Prototypes
    - JavaScript, SELF
    

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33. Delegation IS
    Inheritance
    Lynn Andrea Stein
    OOPSLA 1987
    "Treaty of Orlando"
    

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34. OOP= Objects
    + Encapsulation
    + Polymorphism
    + Inheritance
    

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35. It’s all about
    MESSAGES
    

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36. call a method
    

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37. • delegation
    • method_missing
    call a method
    

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38. send a message
    call a method
    

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39. class Person
    def name; @name; end
    end
    class Employee < Person
    def name; "#{@name}, #{@title}"; end
    end
    class Letter
    # address letter to recipient's name without title
    def recipient_name
    super_name = Person.instance_method(:name)
    bound_name = super_name.bind(@recipient)
    bound_name.call
    end
    end
    

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40. class Person
    def name; @name; end
    end
    class Employee < Person
    def name; "#{@name}, #{@title}"; end
    end
    class Letter
    # address letter to recipient's name without title
    def recipient_name
    super_name = Person.instance_method(:name)
    bound_name = super_name.bind(@recipient)
    bound_name.call
    end
    end
    

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41. use objects
    •blocks & lambdas
    •hashes & arrays
    •symbols (names)
    instead of
    

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42. use objects
    reification unites
    behavior with
    data
    

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43. validation
    validates_presence_of :phone
    validate { |r|
    r.home_phone? || r.cell_phone? }
    validate :validate_has_a_phone
    validates_with HasAPhone
    

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44. polymorphism
    Method lookup is fast.
    Testing class type is slow
    and messy.
    

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45. def scope
    if @product
    if current_api_user.has_spree_role?("admin")
    unless params[:show_deleted]
    variants = @product.variants_including_master
    else
    variants = @product.variants_including_master_and_deleted
    end
    else
    variants = @product.variants_including_master
    end
    else
    variants = Variant.scoped
    if current_api_user.has_spree_role?("admin")
    unless params[:show_deleted]
    variants = Variant.active
    end
    end
    end
    variants
    end
    

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46. def scope
    if @product
    if current_api_user.has_spree_role?("admin")
    unless params[:show_deleted]
    variants = @product.variants_including_master
    else
    variants = @product.variants_including_master_and_deleted
    end
    else
    variants = @product.variants_including_master
    end
    else
    variants = Variant.scoped
    if current_api_user.has_spree_role?("admin")
    unless params[:show_deleted]
    variants = Variant.active
    end
    end
    end
    variants
    end
    

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47. class Variant
    class << self
    alias_method :variants_including_master_and_deleted, :scoped
    alias_method :variants_including_master, :active
    end
    end
    def scope
    scoper = @product || Variant
    if current_api_user.has_spree_role?("admin") && params[:show_deleted]
    scoper.variants_including_master_and_deleted
    else
    scoper.variants_including_master
    end
    end
    

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48. Object = Identity
    + Behavior
    + State
    OOP = Objects
    + Encapsulation
    + Polymorphism
    + Inheritance
    Messages = secret sauce
    

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