This document discusses principles of object-oriented programming maintainability such as reuse of behavior, typing and subtyping, and avoiding repetition. It covers different OOP concepts like classes, inheritance, interfaces, mixins and modules. The document suggests using traits for composing units of behavior in a way that is composable and avoids conflicts. Traits should define smaller interfaces than classes. Specifications can also be composed using shared examples. These principles can be achieved in languages like Java 8+, Ruby and Go.

1. OOPS v2.0.0-rc.1
Aditya Godbole
@aagdbl

2. Definitions
• Type - Set of methods
• Subtype(T) - Superset methods of the type T
• Class - Implementation of type + properties of
implementing object

3. Maintainability

4. Maintainability
Re-use

5. Maintainability
Re-use
of?

7. Behaviour
(not data)

8. Maintainability

9. Maintainability
• Re-use of behaviour

10. Maintainability
• Re-use of behaviour
• Typing and Sub-typing

11. Axes of maintainability

12. Axes of maintainability
Don’t repeat
yourself
(DRY)

13. Axes of maintainability
Don’t repeat
yourself
(DRY)

14. Axes of maintainability
Don’t repeat
yourself
(DRY)
Don’t shoot yourself
(DSY)

15. Maintainability
• Re-use of behaviour
• Sub-typing

16. Maintainability
• Re-use of behaviour
• Sub-typing Granularity

18. Composability
• Behaviour - Inject behaviour from multiple
sources
• Types - Create superset types by combining
smaller types

19. Classes
• Re-use
• Multiple inheritance
• Subtyping (Polymorphism)
• Multiple inheritance

20. Interfaces

21. Interfaces
• Type definitions

22. Interfaces
• Type definitions
• Composable

23. DRY
DSY
Classes /
Inheritance
Interfaces
Java?

24. DRY
DSY
Classes /
Inheritance
Interfaces
Mixins /
Modules
Java?

25. DRY
DSY
Classes /
Inheritance
Interfaces
Mixins /
Modules
Java?
Ruby?

26. DRY
DSY
Classes /
Inheritance
Interfaces
Mixins /
Modules
Java?

27. DRY
DSY
Classes /
Inheritance
Interfaces
Mixins /
Modules
Java?
Ruby?

28. DRY
DSY
Classes /
Inheritance
Interfaces
Mixins /
Modules
Java?
Ruby?
Interfaces?

29. gem install rubycube
require “cube”
Composable Units of
BEhaviour

32. DRY
DSY
Classes /
Inheritance
Interfaces
Mixins /
Modules
Java?
Ruby
Interfaces

33. DRY
DSY
Classes /
Inheritance
Interfaces
Mixins /
Modules
Java?

34. DRY
DSY
Classes /
Inheritance
Interfaces
Mixins /
Modules
Java?
Ruby
Interfaces

35. DRY
DSY
Classes /
Inheritance
Interfaces
Mixins /
Modules
Java?
Ruby
Interfaces
??

36. Conflicts

39. required interface

41. (sum, pos, fact)

43. AdvancedCalc =
SimpleCalcImpl
ProductCalcT
StatsCalcT
- [:product]
+
+
=> AdvancedCalculator

46. Using Traits
• Structural classes - Enforce structural integrity.
• Identify interactions - Create smallest possible
interface
• Traits should be smaller or equal to interfaces
• If required - extend structural class to create
glue class for required interface
• Compose using traits

47. Specs
• Rspec “shared_examples”
• Compose specs using “it_behaves_like”

48. Also achievable …
• Java 8+
• Golang

49. DRY
DSY
Java 8
Interfaces
Traits
Ruby Go

50. __/__
https://github.com/adityagodbole/rubycube
gem install rubycube
(please go and read the traits paper)