Refactoring - Improving the Design of Existing Code

Transcript

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   Refactoring Improving the Design of Existing Code @mehlah

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

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   A video store Customer Movie 1 * 1 * statement()

   daysRented: int Rental priceCode: int
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   A video store aCustomer aRental aMovie *[for all rentals] getMovie

   getPriceCode getDaysRented statement
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   What are your impressions ?

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   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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    Let’s Refactor

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    Before you start refactoring, check that you have a solid

    suite of tests. These tests must be self-checking. Tip
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    Decomposing and Redistributing the Statement Method

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    None
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    Any fool can write code that a computer can understand.

    Good programmers write code that humans can understand. Tip
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    Moving the Amount Calculation

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    None
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    None
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    None
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    State of classes after moving the charge method Customer Movie

    1 * 1 * statement() daysRented: int Rental priceCode: int getCharge()
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    Extracting Frequent Renter Points

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    None
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    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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    aCustomer aRental aMovie *[for all rentals] getCharge getFrequentRenterPoints statement getPriceCode

    getPriceCode
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    Removing Temps

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    None
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    Customer Movie 1 * 1 * statement() daysRented: int Rental

    priceCode: int getCharge() getFrequentRenterPoints() getTotalCharge() getTotalFrequentRenterPoints()
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    aCustomer aRental aMovie getTotalCharge *[for all rentals]getCharge *[for all rentals]

    getFrequentRenterPoints statement getPriceCode getPriceCode getTotalFrequentRenterPoints
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    Replacing the Conditional Logic on Price Code with Polymorphism

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    1. Move getCharge et getFrequentRenterPoints from Rental to Movie class

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    None
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    Movie getCharge() Regular Movie getCharge() Children Movie getCharge() New Release

    Movie getCharge()
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    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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    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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    None
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    3. Replace Movie's getCharge conditional with a type code behavior

    in the Price Object
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    None
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    4. Move getFrequentRenterPoints method from Movie to Price and replace

    conditional with polymorphism
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    Notes Typefaces: Open Sans + Abril GitHub repo (see closed

    Pull Requests) https://github.com/craftsmen/refactoring-php-example
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    Thanks @mehlah