Advanced OOP in Elixir - Speaker Deck

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Advanced OOP in Elixir Wojtek Mach @wojtekmach @wojtekmach

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import OOP

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import OOP class Person do var :name end

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import OOP class Person do var :name end joe = Person.new(name: "Joe") robert = Person.new(name: "Robert")

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import OOP class Person do var :name end joe = Person.new(name: "Joe") robert = Person.new(name: "Robert") joe.name() # => "Joe" robert.name # => "Robert"

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import OOP class Person do var :name def say_hello_to(who) do IO.puts("#{this.name}: Hello, #{who.name}") end end joe = Person.new(name: "Joe") robert = Person.new(name: "Robert") joe.name() # => "Joe" robert.name # => "Robert" joe.say_hello_to(robert) # => Joe: Hello, Robert

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joe = Person.new(name: "Joe") joe.set_name("Hipster Joe") # => :ok joe.name # => "Hipster Joe"

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Q: How does it work? 

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Q: How does it work?  A: You don’t want to know.

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Q: How does it work?  A: Macros.

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some FP programmer: „this is bad code” 

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Perhaps it’s not that bad… 

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Q: What’s worse than OOP? 

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Q: What’s worse than OOP?  A: OOP with inheritance.

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class Shape do var :x var :y end

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class Shape do var :x var :y end class Rectangle < Shape do var :width var :height def area do this.width * this.height end end

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class Shape do var :x var :y end class Rectangle < Shape do var :width var :height def area do this.width * this.height end end class Square < Rectangle do def area do :math.pow(this.width, 2) end end

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Perhaps it’s not that bad… 

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Q: What’s worse than OOP with inheritance? 

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Q: What’s worse than OOP with inheritance?  A: OOP with multiple inheritance.

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class Human do end

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class Human do end class Spider do end

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class Human do end class Spider do end class Spiderman < [Human, Spider] do end

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Advanced OOP

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class Post do end Post.new

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class Post do end class Comment do end Post.new Comment.new

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abstract class ActiveRecord.Base do end class Post < ActiveRecord.Base do end class Comment < ActiveRecord.Base do end Post.new Comment.new

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abstract class ActiveRecord.Base do end class Post < ActiveRecord.Base do end class Comment < ActiveRecord.Base do end Post.new Comment.new ActiveRecord.Base.new ** (RuntimeError) cannot instantiate abstract class ActiveRecord.Base

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abstract class ActiveRecord.Base do end abstract class ApplicationRecord < ActiveRecord.Base do end class Post < ApplicationRecord do end class Comment < ApplicationRecord do end

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class HalfLife do end

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class HalfLife do end class HalfLife2 < HalfLife do end

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class HalfLife do end final class HalfLife2 < HalfLife do end

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class HalfLife do end final class HalfLife2 < HalfLife do end class HalfLife3 < HalfLife2 do end ** (RuntimeError) cannot subclass final class HalfLife2

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class AppleInc do end

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class AppleInc do var :devices end apple = Apple.new(devices: ["Alice's iPhone", "Bob's iPad"]) apple.devices # => ["Alice's iPhone", "Bob's iPad"]

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class AppleInc do private_var :devices end apple = Apple.new(devices: ["Alice's iPhone", "Bob's iPad"]) apple.devices ** (RuntimeError) Cannot access private var devices

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class NSA do def get_data(company, _fisa_court_order \\ nil) do company.devices end end class AppleInc do private_var :devices end apple = Apple.new(devices: ["Alice's iPhone", "Bob's iPad”]) NSA.new.get_data(apple) ** (RuntimeError) Cannot access private var devices

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class NSA do def get_data(company, _fisa_court_order \\ nil) do company.devices end end class AppleInc do friend NSA private_var :devices end apple = Apple.new(devices: ["Alice's iPhone", "Bob's iPad”])