Refactoring - Improving the Design of Existing Code

Inspired by Martin Fowler's Refactoring book.

Transcript

1. Refactoring Improving the Design of Existing Code @mehlah
2. “A change to the system that leaves its behavior unchanged, but enhances some nonfunctional quality – simplicity, flexibility, understandability, performance” Kent Beck, Extreme Programming Explained
3. “A change made to internal structure of software to make it easier to understand and modify without changing its observable behavior.” Martin Fowler, Refactoring
4. “To refactor is to take a bad design, chaos even, and rework it into well-designed code, with baby steps” Mehdi Lahmam B.
5. puts “Show me the code.” puts “Talk is cheap.”
6. A video store Customer Movie 1 * 1 * statement() daysRented: int Rental priceCode: int
7. A video store aCustomer aRental aMovie *[for all rentals] getMovie getPriceCode getDaysRented statement
8. What are your impressions ?
9. When you find you have to add a feature to a program, and the program's code is not structured in a convenient way to add the feature, first refactor the program to make it easy to add the feature, then add the feature. Tip
10. Let’s Refactor
11. Before you start refactoring, check that you have a solid suite of tests. These tests must be self-checking. Tip
12. Decomposing and Redistributing the Statement Method
14. Any fool can write code that a computer can understand. Good programmers write code that humans can understand. Tip
15. Moving the Amount Calculation
19. State of classes after moving the charge method Customer Movie 1 * 1 * statement() daysRented: int Rental priceCode: int getCharge()
20. Extracting Frequent Renter Points
22. After extraction and movement of the frequent renter points calculation Customer Movie 1 * 1 * statement() daysRented: int Rental priceCode: int getCharge() getFrequentRenterPoints()
23. aCustomer aRental aMovie *[for all rentals] getCharge getFrequentRenterPoints statement getPriceCode getPriceCode
24. Removing Temps
26. Customer Movie 1 * 1 * statement() daysRented: int Rental priceCode: int getCharge() getFrequentRenterPoints() getTotalCharge() getTotalFrequentRenterPoints()
27. aCustomer aRental aMovie getTotalCharge *[for all rentals]getCharge *[for all rentals] getFrequentRenterPoints statement getPriceCode getPriceCode getTotalFrequentRenterPoints
28. Replacing the Conditional Logic on Price Code with Polymorphism
29. 1. Move getCharge et getFrequentRenterPoints from Rental to Movie class
31. Movie getCharge() Regular Movie getCharge() Children Movie getCharge() New Release Movie getCharge()
32. Price getCharge Regular Price getCharge Childrens Price getCharge New Release Movie getCharge Movie getCharge return price->getCharge() Using the State pattern [GoF] on movie
33. 2. Add a Price class with subclasses and change movie's accessors for the price code to use the new class
35. 3. Replace Movie's getCharge conditional with a type code behavior in the Price Object
37. 4. Move getFrequentRenterPoints method from Movie to Price and replace conditional with polymorphism
38. Notes Typefaces: Open Sans + Abril GitHub repo (see closed Pull Requests) https://github.com/craftsmen/refactoring-php-example
39. Thanks @mehlah