Refactoring - Improving the Design of Existing Code

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

13. None

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

16. None
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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

21. None

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

25. None

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

30. None

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
34. None

35. 3. Replace Movie's getCharge conditional with a type code behavior

    in the Price Object
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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