Delegation, Forwarding, Inheritance, Composition, Aggregation, … I'm lost !

A overview of these different development design concepts in Ruby.

Transcript

1. Delegation, Forwarding, Inheritance, Composition, Aggregation, … I'm lost ! Ben Colon Geneva.rb, 2014/03/19
2. Ben Colon • Senior Software Engineer @ Gatemedia SA • Former developer, entrepreneur, lead dev & CTO. • But I’m a DEVELOPER :)) • @bcolon
3. Delegation Forwarding Inheritance Composition Aggregation Inheritance vs Delegation Composition vs Aggregation
5. Design Patterns ? • Wikipedia definition […] A design pattern is a general reusable solution to a commonly occurring problem within a given context in software design.
6. Design Patterns Classification • « The Gang of four » classification • Creational patterns • Structural patterns • Behavioral patterns
7. Design Patterns Classification • Creational patterns • Factory method pattern, Abstract factory pattern, Singleton pattern, Builder pattern, Prototype pattern, … • Structural patterns • Adapter pattern, Bridge pattern, Composite pattern, Decorator pattern, Facade pattern, Flyweight pattern, Proxy pattern, … • Behavioral patterns • Chain-of-responsibility pattern, Command pattern, Interpreter pattern, Iterator pattern, Mediator pattern, Memento pattern, Observer pattern, State pattern, Strategy pattern, Template method pattern, Visitor pattern, …
8. But … we still haven’t find Delegation, Composition, Forwarding, Aggregation or Inheritance terms !
9. Design Patterns Design « Concepts » • Inheritance, Composition, Aggregation • « Reusability » concepts • Delegation, Forwarding • « Behaviour » concepts
10. Used by design patterns • Creational patterns • Factory method pattern, Abstract factory pattern, Singleton pattern, Builder pattern, Prototype pattern, … • Structural patterns • Adapter pattern, Bridge pattern, Composite pattern, Decorator pattern, Facade pattern, Flyweight pattern, Proxy pattern, … • Behavioral patterns • Chain-of-responsibility pattern, Command pattern, Interpreter pattern, Iterator pattern, Mediator pattern, Memento pattern, Observer pattern, State pattern, Strategy pattern, Template method pattern, Visitor pattern, … Delegation Inheritance Composition, Inheritance
11. Dive into these « reusability » concepts • Inheritance : a class is based on another class
 « Is a » relationship • Composition : one object containing another one
 « Has a » relationship • Aggregation : one object using another one
 « Uses a » relationship
12. Inheritance in Ruby • Ruby has single inheritance. Each class has one and only one parent class Implicit Inheritance Override Inheritance Altered Inheritance
13. Composition in Ruby • « Has a » relationship
14. Aggregation in Ruby • « Uses a » relationship • Wikipedia says « Composition is where a structure directly includes its members, whereas Aggregation is where a structure only contains references to those members. » • In Ruby everything is object, so Aggregation is the same as Composition. • For C++ fans, just a * difference
15. Dive into these « behavioral » concepts • Delegation on Wikipedia « An object, instead of performing one of its stated tasks, delegates that task to an associated helper object. » • Forwarding ? Nothing on Wikipedia but in Delegation page « this mechanism is sometimes referred to as forwarding » :) • DELEGATION = FORWARDING … semantically
16. Delegation/Forwarding in Ruby • Several librairies/classes in Ruby : • Delegator, SimpleDelegator, DelegateClass • Forwardable & SingleForwardable • And in Rails, ActiveSupport::Delegation module
18. require ‘delegate' 
 vs 
 require 'forwardable' • Delegate 
 allows you to delegate methods to a class,
 by class basis • Forwardable
 allows you to delegate specified methods to a class, 
 by method basis
19. require 'delegate' • Delegator • Full control over the delegation scheme
20. require 'delegate' • SimpleDelegator • Easiest way. Pass an object to the constructor and all methods supported by the object will be delegated
21. require 'delegate' • DelegateClass • Use to setup delegation at class definition
22. require 'forwardable' • Forwardable • Use to setup specified delegation at class level
23. require 'forwardable' • SingleForwardable • Use to setup specified delegation on object itself, instead of the defining class
24. ActiveSupport Delegation • Delegate method • Rather similar to the Forwardable lib • More options
25. Comparaisons • Delegation vs Forwarding • Composition vs Aggregation • Inheritance vs Delegation • Inheritance vs Composition
26. Bad/Good comparaisons • Delegation vs Forwarding • Composition vs Aggregation • Inheritance vs Delegation • Inheritance vs Composition
27. Inheritance vs Composition • « Favor object composition over class inheritance » The Gang of Four • More reusable, more flexible, better testability • A first guideline, « has a » composition, « is a » inheritance • But Liskov Substitution Principle seems to be more accurate
28. Don’t forget the Mixins • Great tool to build Composition • « Mixins are the multiple inheritance facility I had dreamed about » An anonymous C++ developer.
29. Overview « Gang of Four »Design patterns Inheritance Composition/Aggregation Delegation/Forwarding Mixins
30. Conclusion Subjectivity !
31. Books
32. Sources • Wikipedia, StackOverflow & Ruby Documentation • Unleash the Secrets of the Standard Library with SimpleDelegator, Forwardable and more. • Re-use in OO: Inheritance, Composition and Mixins • Inheritance Vs. Composition