[PL] Class instance variables. RRUG #2

Difference between class variables and instance variables, how to use them properly with mixins. Talk given during a meeting of Rzeszów Ruby User Group (RRUG).

Transcript

1. CLASS INSTANCE VARIABLES
   RZESZÓW RUBY USER GROUP #2
   30.11.2016
   Maciej Rząsa
   PGS Software
   @mjrzasa
   

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2. KLASOWE CZY
   INSTANCYJNE?
   

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3. ZMIENNE INSTANCYJNE
   class Book
   attr_accessor :author, :title
   def info
   "#{@author}: #{@title}"
   end
   end
   b1 = Book.new
   b1.author = "Adam Mickiewicz"
   b1.title = "Dziady"
   b1.info # => "Adam Mickiewicz: Dziady"
   b2 = Book.new
   b2.author = "Jan Kochanowski"
   b2.title = "Pieśni"
   b2.info # => "Jan Kochanowski: Pieśni"
   

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4. ZMIENNE KLASOWE
   class Book
   @@counter = 0
   def initialize
   @@counter += 1
   end
   def self.counter
   @@counter
   end
   def info
   @@type
   end
   end
   Book.new
   Book.new
   Book.counter # => 2
   

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5. ZMIENNE KLASOWE: DZIEDZICZENIE
   class Book
   @@counter = 0
   def initialize
   @@counter += 1
   end
   def self.counter
   @@counter
   end
   def info
   @@type
   end
   end
   class Novel < Book
   def initialize
   super
   end
   end
   Book.new
   Book.new
   Book.counter # => 2
   Novel.new
   Book.counter # => 3
   

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6. ZMIENNE KLASOWE: DZIEDZICZENIE
   class Book
   def self.available_genres(*genres)
   @@available_genres = genres
   end
   def self.show_available_genres
   @@available_genres
   end
   available_genres :novel, :poetry, :drama
   end
   Book.show_available_genres
   # => :novel, :poetry, :drama
   class Novel < Book
   available_genres :historical, :contemporary, :futuristic
   end
   Novel.show_available_genres
   # => :historical, :contemporary, :futuristic
   # => yay!
   Book.show_available_genres
   # => :historical, :contemporary, :futuristic
   # => ups...
   

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7. KLASOWE ZMIENNE INSTANCYJNE
   class Book
   def self.available_genres(*genres)
   @available_genres = genres
   end
   def self.show_available_genres
   @available_genres
   end
   available_genres :novel, :poetry, :drama
   end
   Book.show_available_genres
   # => :novel, :poetry, :drama
   class Novel < Book
   available_genres :historical, :contemporary, :futuristic
   end
   Novel.show_available_genres
   # => :historical, :contemporary, :futuristic
   # => yay!
   Book.available_genres
   # => :novel, :poetry, :drama
   # => yay!
   

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8. PODSUMOWANIE
   zmienne klasowe
   @@var
   wspólne dla hierchii klas
   dostępne w instancjach bezpośrednio (@@var)
   klasowe zmienne instancyjne
   @var w ciele klasy albo metody klasowej
   prywatne dla danej klasy
   dostępne w klasie, w instancjach tylko przez metody
   klasowe
   

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9. W MODUŁACH
   module Options
   def available_options(*options)
   @@available_options = options
   end
   def show_available_options
   @@available_options
   end
   end
   class Book
   extend Options
   available_options :novel, :drama, :poetry
   end
   Book.show_available_options
   # [ :novel, :drama, :poetry ]
   class Job
   extend Options
   available_options :developer, :tester, :manager
   end
   Job.show_available_options
   # => [ :developer, :tester, :manager ]
   Book.show_available_options
   # => [ :developer, :tester, :manager ]
   

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10. W MODUŁACH
    module Options
    def available_options(*options)
    @available_options = options
    end
    def show_available_options
    @available_options
    end
    end
    class Book
    extend Options
    available_options :novel, :drama, :poetry
    end
    Book.show_available_options
    # => [ :novel, :drama, :poetry ]
    class Job
    extend Options
    available_options :developer, :tester, :manager
    end
    Job.show_available_options
    # => [ :developer, :tester, :manager ]
    Book.show_available_options
    # => [ :novel, :drama, :poetry ]
    

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11. PODSUMOWANIE
    dwa typy zmiennych w klasie
    @@klasowe są wspólne dla hierarchii klas
    @instancyjne są prywatne dla klasy (bo klasa jest
    obiektem)
    ważne przy modułach dodających metody klasowe
    

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