OO without Inheritance

My talk from @RedFrogConf – the Ruby Subconference

Transcript

1. RWTH Aachen, Computer Science Student triAGENS GmbH, Developer moon lum moonbeamlabs by Lucas Dohmen OO Without Inheritance and the Treaty of Orlando
2. Who is that uy? • Aran oDB Core Team • Aran oDB Foxx & Ruby Adapter • Student on the master branch • hacken.in & nerdkun.de /\ (~( ) ) /\_/\ ( _-----_(@ @) ( \ / /|/--\|\ V " " " "
3. Software Architectures: Lessons • All the rules I learned are useless, because they were way to eneral • UML is not a ood fit for architectures • OO is not a ood idea
4. OO is not a ood idea? • The professor is an emeritus prof • For him, the Smalltalkers were the new kids on the block • For him, OO == Inheritance • And it‘s quite interestin why
5. What is OO? Spoiler: I don‘t know
6. “ The bi idea is messa in Alan Curtis Kay
7. Object = Identity + Behavior + State (stolen from Josh Susser) OOP = Objects + Encapsulation + Polymorphism + Inheritance
8. OOP = Objects + Encapsulation + Polymorphism + Inheritance
9. OOP = Objects + Encapsulation + Polymorphism + Inheritance
10. OOP = Objects + Encapsulation + Polymorphism + Inheritance
11. OOP = Objects + Encapsulation + Polymorphism + Inheritance
12. OOP = Objects + Encapsulation + Polymorphism + Inheritance
13. Inheritance in Ruby
14. class A < B end
15. class A end p A.ancestors # => [A, Object, Kernel, BasicObject]
16. class A end module M end class B < A include M end p B.ancestors # => [B, M, A, Object, Kernel, BasicObject]
17. Inheritance: The U ly Parts
18. “ Inheritance is hard because classifyin is hard Prof. Dr.-In . Dr.h.c. Manfred Na l
19. The “School Example” for Inheritance • There are birds • Birds can fly • A oose is a bird – it therefore can fly
20. Implementation • We have an abstract class called Bird, it implements the fly method • We have a class Goose, it inherits from Bird
21. Source: http://dosefun.com
22. Ok -.- • We introduce a new abstract class called BirdsThatCantFly inheritin from Bird • In this class we overwrite the fly method to raise an exception
23. Source: http://ironsidebirdrescue.blo spot.de
24. Come on… o_o • We introduce a new class called GooseWithWoundedWin inheritin from Goose • In this class we overwrite the fly method to raise an exception
25. <abstract> Bird Dove <abstract> BirdThatCantFly WoundedDove Kiwi Duplication
26. Generated with: http://meme enerator.net
27. Extract the win ! Leave that bird alone! I mean the class Win !
28. class CantFlyException < RuntimeError end class WoundedWing def fly raise CantFlyException, "Wing is wounded" end end class Wing def fly puts "If only I was an African swallow, I could carry a coconut." end end class Dove def initialize(wing) @wing = wing end def fly @wing.fly end end }We have Forwardable in the STD lib for that
29. wing = Wing.new dove_1 = Dove.new(wing) dove_1.fly # => If only I was an African swallow, I could carry a coconut. broken_wing = WoundedWing.new dove_2 = Dove.new(broken_wing) dove_2.fly # => Wing is wounded (CantFlyException)
30. Reuse • You can now reuse the Win class for different animals, includin birds • You can exchan e the wounded win with a healthy one when it ets cured • You can do win -size and wei ht specific calculations for speed (yep, yep)
31. Ruby • In Java you would need to introduce interfaces now • Questionable result • But we‘re oose typin
32. This was a simple example • But it applies too so many class hierarchies • Especially when requirements chan e • And requirements always chan e…
33. Why is Dele ation better? Or: The Treaty of Orlando
34. What is the Treaty of Orlando? • It‘s a short paper from ’87 that unites the results of three papers • It‘s written by the authors of the papers themselves: Henry Liebermann, Lynn Andrea Stein and David Un ar • … and it ends with the sentence: “this a reement shall henceforth be known as the TREATY OF ORLANDO.” :)
35. Dele ation is Inheritance • Dele ation is exactly the same thin as inheritance • It includes prototypical inheritance introduced in David Un ar‘s Self (now well known for its usa e in JavaScript)
36. It‘s a classification • With the treaty of Orlando you can classify an inheritance / dele ation system • There are three attributes to distin uish
37. Static or Dynamic? • Static systems require determinin the sharin patterns by the time an object is created • Dynamic systems permit determination of sharin patterns durin runtime, when an object actually receives a messa e
38. Implicit or Explicit • Implicit systems dele ate anythin that can‘t be handled locally • Explicit systems have the ability to dele ate only a sin le method
39. Per Object or Per Group • Per roup means that a roup of objects (a class f.e.) all inherit the same way • Per object means that the inheritance is defined for a specific object
40. Let‘s apply that to Ruby‘s systems
41. Inheritance / Module Inclusion Forwardable Dynamic* Dynamic Implicit Explicit Per Group Per Object
42. IMHO • Explicit inheritance helps a lot when you search for the method definition • Per object inheritance is much easier to mock • You can also chan e the dele ation tar et at runtime (when the win ets cured) • Therefore Ruby‘s Forwardable is the better inheritance mechanism in Ruby
43. Inheritance: The Good Parts
44. Inheritin class methods • Ruby has a beautiful feature: Class methods can be called in the body of a class • This is a buildin block for a lot of DSLs • I think there‘s nothin wron with that
45. class User include Virtus attribute :first_name, String attribute :age, Integer attribute :birthday, DateTime end
46. This is beautiful • … and you should use it • I would however wish that you could mark class methods as “protected” in Ruby
47. What about Frameworks? • A difficult question • If you reimplement all hooks it needs, you have a lot of code duplication • But you still have the same problems with testin etc. • Keep the herita e small (Lookin at you, ActiveRecord)
48. Wrappin Up • Is it still OOP if I don‘t use inheritance? I honestly don‘t know (Who cares) • Use inheritance wisely • Don‘t use inheritance for the thin s you were tau ht to use it for
49. moon lum moonbeamlabs kthxbye