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Reduce Reuse Refactor
This document discusses strategies for refactoring legacy code to improve its design and maintainability. It defines refactoring as changing code structure without altering functionality. The key steps outlined are to first add new functionality, then refactor, then add more functionality. Code "smells" that indicate areas for refactoring include duplicate code, long methods, large classes, and more. Tools can help detect smells. Technical debt should be paid off incrementally by refactoring in small batches while ensuring tests pass. Specific refactoring techniques include autoloading, consolidating classes, removing globals, replacing instantiation with factories, extracting logic, and more. Testing is important throughout the refactoring process.
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Reduce Reuse Refactor
- 1. Reduce, Reuse, Refactor improvingthe design of existing code
- 2. GOAL != “Perfection” GOAL== “Improvement”
- 3. What is “LegacyCode” Is there a coding standard for your project? Is code using OOP? Is Composer used in your project? Are you unit testing? Does your project avoid NIH?
- 4. What is “refactoring”? “…processof changing a computer program’s source code without modifying its external functional behavior…” No functionality added Code quality
- 5. Two Hats adding functionalityhat refactoring hat we add functionality, then refactor, then add more functionality
- 6. Then optimize Do notoptimize while refactoring Separate step Refactoring is NOT optimizing
- 7. Why refactor? Prevent decay Preserveor fix design Reduce duplication Improve maintainability Helps us code faster Locate bugs Code smells
- 8. What are code“smells”? Indications of spoiled code nearby Not conclusive The “smell” is not bad “Potential” problems
- 9. Code “smells” hintsto refactor Duplicate Code (rule 3) Long Methods Large Class Long Parameter (argument) List Divergent Change - cascade change to accommodate another Shotgun Surgery - change ripples as bugs Feature Envy - methods uses parts from other class Switch Statements - sacrifice polymorphism
- 10. Code “smells” hintsto refactor: 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 price parts Data Class - getters and setters, but nothing else Comments - where comments cover bad code
- 11. Tools to highlightsmells PHPqatools.org PHPUnit PHPLoc PHP_Codesniffer PHP_Depend PHP Copy/Paste Detector PHP Mess Detector PHP Dead Code Detector Zend Z-Ray: realtime profiling
- 13. Paying off technicaldebt a lot like paying off financial debt got the stuff first, but have to pay for it eventually must pay off technical debt not of our own choosing suffering as things are, or suffering through change
- 14. Declare Bankruptcy rewrite fromscratch! expend effort while not earning revenue old devs on new project? new devs on new project takes longer than you think end up with different bad architecture
- 15. When to rewrite Wanta new app Not just better coded current app Business logic change Target market change Framework integration or change
- 16. Incremental approach pay offsmallest debt first (build inertia and raise spirits) small changes across codebase build on previous small changes improve quality over time Embrace incremental change
- 17. When to refactor No“special” time Short bursts Refactor to gain something Prior to adding functionality When fixing a bug During code review ninjagrl.com
- 18. Before You start Getit working! Use source control (Git, SVN, etc.) Use an IDE Follow a Style Guide Have Tests in place
- 19. Source Control Refactor inbranch Allows rollback
- 20. Editor/IDE Makes searching easier Searchwithin project
- 21. Style Guide Framework InteropGroup http://php-fig.org PSR Faster reading United team
- 22. Testing Consistent results Prevents breaks Speedsup development
- 23. Refactor, Test, Repeat Ensuretests pass Plan and implement refactor Ensure tests still pass Updating test if needed Add more tests to cover newly discovered items Repeat!
- 24. Modernizing Steps Autoloading Consolidate Classes CleanupGlobals Replace “new” (instantiation) Create Tests Extract SQL Extract Domain Logic Extract Presentation Logic Replace Remaining “Includes”
- 25. Autoloading Approaches PSR-0 orPSR-4 Approaches Global function Closure Static or Instance Method (preferred, if possible) __autoload() - PHP v 5.0 Need a central place for classes
- 26.
- 27. Consolidate Classes Step 1 Searchfor include statements (include, include_once, require, require_once) Step 2 Move into central location (“includes”, “classes”, “src”, “lib”, etc.) Step 3 Implement autoloading (no more include statements for classes)
- 28.
- 29. Cleanup “Global” DependenciesStep 1. Search for global reference 2. Move global calls to constructor 3. Convert global call to a constructor parameter 4. Update global call to a class 5. Instantiate new class and pass as parameter (DI)
- 30.
- 31. Steps to Replace“new” 1. Search for “new” 2. Extract instantiation to constructor parameter. (if one time) Or extract block of creation code to new Factory class. (if repeated) 3. Update instantiation calls
- 32.
- 33. Write Tests Code isfairly clean Write tests for entire application If not testable, refactor Extract method Replace temp with query Etc.
- 34.
- 35. Extract SQL 1. Searchfor SQL 2. Move Statement and relevant logic to Gateway class 3. Create test for new class 4. Alter code to use new method
- 36.
- 37. Extract Domain Logic Searchfor uses of Gateway class outside of Transaction classes Extract logic to Transaction classes
- 38.
- 39. Extract Presentation Logic Setupyour Views Should have MINIMAL logic May use templating such as Twig Allows UI designers to own that code
- 40.
- 41. Replace leftover “includes” Ifin current class Copy contents into file directly Refactor for: no globals, no ‘new’, DI, return instead of output, no includes More often Copy contents of includes as-is to new class method Replace with in-line instantiation Search for other uses of same, and update them as well Delete original include file, regression test
- 42.
- 43. Initial Goals Completed Consolidatedinto classes with autoloading Remove globals in favor of dependency injection Kept it running the whole time Paid off some technical debt Organizational structure for future work Started writing unit tests
- 44. Additional Possibilities Can nowimplement framework Leverage services Leverage events Use Composer
- 45. Concluding Thoughts Do notrefactor a broken application Have tests in place prior to refactoring Unit Tests Functional test Manual tests Do things in small steps Leave the code better than you left it
- 47.
- 48. Alena Holligan • Wife,and Mother of 3 young children • PHP Teacher at Treehouse • Portland PHP User Group Leader • Cascadia PHP Conference (cascadiaphp.com) @alenaholligan alena@holligan.us https://joind.in/talk/efa39