Refactoring 101

Refactoring 101 By: Adam Culp Twitter: @adamculp https://joind.in/14927

Refactoring 101 ● 2 About me – PHP 5.3 Certified – Consultant at Zend Technologies – Organizer SoFloPHP (South Florida) – Organized SunshinePHP (Miami) – Long distance (ultra) runner – Judo Black Belt Instructor

Refactoring 101 ● Fan of iteration – 3 Pretty much everything requires iteration to do well: ● Long distance running ● Judo ● Development ● Evading project managers ● Refactoring!

Refactoring 101 ● 4 About talk – Based on “Refactoring; Improving The Design of Existing Code” book, by Martin Fowler. – https://github.com/adamculp/refactoring101 – for PHP code samples

Refactoring 101 ● 6 What is “refactoring”? – “…process of changing a computer program’s source code without modifying its external functional behavior…” en.wikipedia.org/wiki/Refactoring – Should not add functionality – Simplify code – Improve code readability

Refactoring 101 ● 7 Two hats – Adding Functionality Hat – Refactoring Hat – We add functionality, then refactor, then add more functionality …

Refactoring 101 ● 8 Then optimize – Do not optimize while refactoring – Separate step – Refactoring is NOT optimizing

Refactoring 101 ● 9 Why refactor? – Prevent decay – Preserve or fix design – Reduce duplication – Improve maintainability – Helps us code faster – Locate bugs – Code smells

Refactoring 101 ● Code “smells” – 10 What are “smells”? ● Indications of spoiled code nearby ● Not conclusive ● The “smell” is not bad

Refactoring 101 ● Code “smells” – 11 “Smells” hinting a refactor may be needed: ● Duplicate Code (rule of 3) ● Long Methods ● Large Class ● Long Parameter (argument) List ● Divergent Change – cascade change to accommodate another ● Shotgun Surgery – change ripples as bugs ● Feature Envy – method uses parts from other class ● Switch Statements – sacrifice polymorphism

Refactoring 101 ● Code “smells” – 12 Cont’d: ● Lazy Class – class not doing much ● Speculative Generality – something built for possible future ● Temporary Field/Variable ● Message Chains – object asking object asking object ● Middle Man – directors in place but serve no real purpose ● Inappropriate Intimacy – classes share private parts ● Data Class – getters and setters, but nothing else ● Comments – where comments cover bad code

Refactoring 101 ● Tools to highlight smells – 14 PHPqatools.org ● PHPUnit ● PHPLoc ● PHP_Codesniffer ● PHP_Depend ● PHP Copy/Paste Detector ● PHP Mess Detector ● PHP Dead Code Detector

Refactoring 101 ● Realtime profiling – 15 Zend Z-Ray

Refactoring 101 ● 16 Rewrite vs Refactor – Rewrite = perceived easy road – Refactor = best teacher – Business arguments ● Budget ● Time ● Retain business logic

Refactoring 101 ● When to rewrite – Want a new app ● 17 Not just better coded current app – Business logic change – Target market change – Framework integration or change

Refactoring 101 ● 18 When to refactor? – No “special” time – Short bursts – Refactor to gain something – Prior to adding functionality – When fixing a bug – During code review

Refactoring 101 ● What do I tell my manager? (justification) – Tech savvy manager = not be hard to explain the benefits. – Quality centric manager = stress quality aspects. – 19 ● Introduce as a review process. ● Many resources on Google. Schedule driven manager = Don’t tell (controversial?). ● Find a way to work it in. ● Overall it saves time, but some will never “see” it.

Refactoring 101 ● First steps – – Use source control (Git, SVN, etc.) ● Records steps, provides rollback ● Auditable GET IT WORKING ● 20 Do NOT refactor broken – Create consistent data – Create tests

Refactoring 101 ● Tests and refactoring – Basic refactor steps ● Ensure tests pass ● Plan refactor ● Implement ● Ensure tests still pass Updating tests if needed – Add more tests to cover newly discovered items Repeat! – ● 21

Refactoring 101 ● Example – Lets look at a code example. – Tips and descriptions during steps. – Our Task: ● Video Rental Company has asked for an HTML representation of their customer statement to be created. Let’s look at the code! 22

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Refactoring 101 ● Code summary: What did we see? – 29 Method → statement() ● Too long ● Not reusable for HTML version ● Switch sacrificing polymorphism ● Determining class/type ● Calculating rental price, frequent renter points, grant total

Refactoring 101 ● 30 Additional notes – Cannot change how movies are classified. – Customers always changes, not easy in current state. ● Movie classification ● Frequent renter points ● Rental days per type ● Price calculation

Refactoring 101 ● Objective: – Clean up statement(). ● Shorten – – 31 Extract code to encapsulate functionality Extract business logic to keep DRY

Refactoring 101 ● 32 TEST ! ! !

Refactoring 101 ● Extract method – 33 Moves a functionality to it’s own method. ● Encapsulate calculation of each rental. ● Shorten statement() method.

Refactoring 101 ● Extract method cont’d. – 34 We now have a new method amountFor().

Refactoring 101 ● 35 Rename variables – Renaming $each to $rental – Improves readability. – Relate intent.

Refactoring 101 ● Renaming variables, cont’d. – 36 Renamed $each to $rental, and also changed $thisAmount to become $result for clarity.

Refactoring 101 ● 37 Rename method – Rename amountFor() to getCharge(). – Self documenting.

Refactoring 101 ● Move method – Move getCharge() from Customer to Rental. ● – 38 Relies on Rental data. Already have Rental object, no need to pass $rental.

Refactoring 101 ● Move method cont’d – Now calls getDaysRented() directly. – Returns charge of Rental, as it should. ● 39 Building rental charge in customer was misplaced.

Refactoring 101 ● Replace temp with query – 40 Remove temporary variable and call Rental->getCharge() direct. ● Less future maintenance. ● Makes code clearer.

Refactoring 101 ● Extract method – 41 $frequentRenterPoints calculation extracted to getFrequentRenterPoints(), and move it in the Rental class.

Refactoring 101 ● 42 Replace temp with query – Encapsulate logic and generation of grand total. – Promotes DRY. – Remove $totalAmount temporary variable.

Refactoring 101 ● 43 Replace temp with query – Encapsulate logic and generation of frequent renter points. – Promotes DRY. – Remove $frequentRentalPoints temporary variable.

Refactoring 101 ● 44 Create HTML statement – Create HTML version. – Rename original as text version.

Refactoring 101 ● Execution – 45 Can call either Text or HTML versions.

Refactoring 101 ● Recap – – – Most refactoring reduces code ● More self-documenting ● More flexibility ● More testable 3 loops (getFrequentRenterPoints, getTotalCharge, and statement) ● Isolates calculations ● Enabled multiple statements (text/html) Optimizing and refactoring = different ● – 46 Refactor, then optimize Future = separation of concerns

Refactoring 101 ● 59 Conclusion – Do not refactor a broken application – Always have tests in place prior to refactor ● Unit tests or ● Functional tests or ● Manual tests – Leave code cleaner than you got it – Try NOT to rewrite – Learn to “smell” problems – Love iteration!

● Thank you! – Code: https://github.com/adamculp/refactoring101 – Please rate at: https://joind.in/14927 Adam Culp http://www.geekyboy.com http://RunGeekRadio.com Twitter @adamculp