Object-Oriented Design

Transcript

1. Object-oriented Rails Brian Reath CCI Systems, Inc. Wednesday, August 15, 12
2. Overview • History • OO Principles • Applying OO to Rails • Exercises Wednesday, August 15, 12
3. History • Gang of Four • Design Patterns: Elements of Reusable Object-Oriented Software • Agile Movement • http://agilemanifesto.org/principles.html Wednesday, August 15, 12
4. GoF Patterns • Factory • Singleton • Adapter • Decorator • Facade • Proxy • Singleton • Observer • Strategy • Iterator Wednesday, August 15, 12
5. Motivation • The only constant is change • Making changes to the application shouldn’t be hindered by our practices • Predicting change is hard Wednesday, August 15, 12
6. Principles • Single Responsibility (SRP) • Small Methods • Reduce Coupling • Limit Use of Globals and Singletons • Small Interfaces with Simple Signatures • Prefer Composition over Inheritance Wednesday, August 15, 12
7. Single Responsibility • Every object in the system should perform one conceptual “responsibility” • Classes should be small and focused • The less an object does, the easier it is to change (or remove) Wednesday, August 15, 12
8. Small Methods • Rambling, conditional logic is hard to follow • Algorithms should be thought about and broken down into steps • Steps should be given names • Individual steps can be ‘stubbed’ in tests • Steps can be reused from different algorithms Wednesday, August 15, 12
9. Reduce Coupling • Having many collaborators is a maintenance nightmare • Changes in one object ripple throughout the system Wednesday, August 15, 12
10. Applied OO • Presenter Pattern (Applied SRP) • Take view-specific logic out of models • Place in custom formatting object • Make use of view layer helpers Wednesday, August 15, 12
11. Applied OO • Service Pattern (Applied SRP) • Remove business logic from AR • Move into application-specific business logic objects • Detach from AR concerns such as callbacks, validations, etc. Wednesday, August 15, 12
12. Applied OO • Strategy Pattern (Coping with Change) • Abstract algorithms into “Strategy” classes • Calculations can be performed in one way initially, but new “strategies” can be plugged in should requirements change Wednesday, August 15, 12
13. Applied OO • Dependency Injection (Code to Interface) • Pass dependencies into object, through constructor or setter method • Implementations can be changed at runtime • Tests can stub out heavyweight implementations Wednesday, August 15, 12
14. Applied OO • Composition (Reduce Coupling) • Subclasses are tightly coupled to superclass • Use instances of the class rather than inheritance Wednesday, August 15, 12
15. Applied OO • Delegation (Reduce Coupling) • Composed objects can be exposed via method calls • “Delegate” calls to wrapped objects Wednesday, August 15, 12
16. You Ain’t Gonna Need It (YAGNI) Wednesday, August 15, 12
17. References • Design Patterns (GoF) • Design Patterns in Ruby Wednesday, August 15, 12