Refactoring - Improving the Design of Existing Code

Inspired by Martin Fowler's Refactoring book.

Transcript

1. Refactoring
   Improving the Design of Existing Code
   @mehlah
   

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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
   

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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
   

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4. “To refactor is to take a bad design, chaos
   even, and rework it into well-designed
   code, with baby steps”
   Mehdi Lahmam B.
   

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5. puts “Show me the code.”
   puts “Talk is cheap.”
   

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6. A video store
   Customer
   Movie
   1 *
   1
   *
   statement()
   daysRented: int
   Rental
   priceCode: int
   

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7. A video store
   aCustomer aRental aMovie
   *[for all rentals]
   getMovie
   getPriceCode
   getDaysRented
   statement
   

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8. What are
   your impressions ?
   

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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
   

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10. Let’s Refactor
    

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11. Before you start refactoring, check that
    you have a solid suite of tests. These
    tests must be self-checking.
    Tip
    

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12. Decomposing and Redistributing
    the Statement Method
    

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14. Any fool can write code that a computer
    can understand. Good programmers
    write code that humans can understand.
    Tip
    

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15. Moving the Amount Calculation
    

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19. State of classes after moving the charge
    method
    Customer
    Movie
    1 *
    1
    *
    statement()
    daysRented: int
    Rental
    priceCode: int
    getCharge()
    

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20. Extracting Frequent Renter
    Points
    

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22. After extraction and movement of the frequent renter
    points calculation
    Customer
    Movie
    1 *
    1
    *
    statement()
    daysRented: int
    Rental
    priceCode: int
    getCharge()
    getFrequentRenterPoints()
    

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23. aCustomer aRental aMovie
    *[for all rentals]
    getCharge
    getFrequentRenterPoints
    statement
    getPriceCode
    getPriceCode
    

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24. Removing Temps
    

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26. Customer
    Movie
    1 *
    1
    *
    statement()
    daysRented: int
    Rental
    priceCode: int
    getCharge()
    getFrequentRenterPoints()
    getTotalCharge()
    getTotalFrequentRenterPoints()
    

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27. aCustomer aRental aMovie
    getTotalCharge
    *[for all rentals]getCharge
    *[for all rentals]
    getFrequentRenterPoints
    statement
    getPriceCode
    getPriceCode
    getTotalFrequentRenterPoints
    

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28. Replacing the Conditional Logic
    on Price Code with Polymorphism
    

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29. 1. Move getCharge et getFrequentRenterPoints from Rental to Movie class
    

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31. Movie
    getCharge()
    Regular Movie
    getCharge()
    Children Movie
    getCharge()
    New Release Movie
    getCharge()
    

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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
    

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33. 2. Add a Price class with subclasses and change movie's accessors for the price code to use the new class
    

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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
    

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38. Notes
    Typefaces: Open Sans + Abril
    GitHub repo (see closed Pull Requests)
    https://github.com/craftsmen/refactoring-php-example
    

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39. Thanks
    @mehlah
    

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