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Refactoring, 2nd Edition
This document discusses refactoring and summarizes the key points from Martin Fowler's book Refactoring. It covers what refactoring is, when it should be used by recognizing code smells, and how it should be done through small, incremental changes backed by thorough testing. The benefits of refactoring include improving code quality by reducing bugs and technical debt, while making the code easier to understand and modify. Tools now make refactoring easier by providing code analysis, refactoring suggestions, and quick fixes.
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Refactoring, 2nd Edition
- 1. Refactoring, 2nd Ed. Alove story Michael Hunger
- 2.
- 3. I know what you'rehere for! Covers By: dev.to/rly
- 4. It crashed at940!
- 5. Which Refactoring doyou like most? Extract Method Delete Unused Code Ok, you won :)
- 7. Questions?! 1. Who hasseen the Refactoring book in a shelf? 2. Who has read it? 3. Who thought that it's just common sense? 4. Who refactors code on a daily basis? 5. Who mentors new developers?
- 8. “Any fool canwrite code that a computer can understand. Good programmers write code that humans can understand.” M. Fowler (1999)
- 9. My Refactoring Story Started18 years ago
- 10. Martin Fowler Foreword byErich Gamma Contributions by Kent Beck, William Opdyke, Don Roberts 28. Juni 1999
- 12.
- 13. I really likedthat book too!
- 14. As did others... … e.g. authors!
- 19. My Student thesisat TU Dresden
- 20. Student thesis at TUDresden "" bit.ly/refactoring-thesis
- 22. Refactoring Tools forJava in 2000!
- 26. Fast Forward 18years
- 27.
- 28. Michael, I'm Martin Fowler'seditor at Addison-Wesley. We are working on a revision of his Refactoring book. Martin suggested that I reach out to you about reviewing the manuscript. He was very impressed with feedback you've provided on other projects. Thanks, Greg -- Gregory Doench Executive Editor Pearson Technology Group
- 29. Several Weeks and435 Pages later
- 30. 28. November 2018 LatestMemo: Most people will be disappointed by the second edition martinfowler.com/articles/refactoring-2nd-ed.html
- 31. Like the original,this edition explains what refactoring is; why you should refactor; how to recognize code that needs refactoring; and how to actually do it successfully, no matter what language you use. ● Understand the process and general principles of refactoring ● Quickly apply useful refactorings to make a program easier to comprehend and change ● Recognize “bad smells” in code that signal opportunities to refactor ● Explore the refactorings, each with explanations, motivation, mechanics, and simple examples ● Build solid tests for your refactorings ● Recognize tradeoffs and obstacles to refactoring
- 32. Why a newbook?
- 33. Refactoring is asimportant as ever Educate a new generation!
- 34.
- 35. No one knowsanymore what video rentals are!
- 36.
- 37. Book Structure (Basicallythe same) 1. Opening Narrative Example Theatre Invoicing 2. Principles 3. Code Smells 4. Testing 5. Catalogue a. most important ones first b. other refactorings 6. Dropped tangential topics and big refactorings
- 38. Refactoring Changes "Split TemporaryVariable" => "Split Variable" "Extract Method" => "Extract Function" Add Parameter, Remove Parameter, Rename Method => Change Function Declaration
- 39. Extract Function Inline Function ExtractVariable Inline Variable Rename Variable Encapsulate Variable Highlighted: Most important Refactorings Migrate Function Declaration Change Function Declaration Introduce Parameter Object Combine Functions into Class Combine Functions into Transform
- 41. New Refactorings All aboutFunctions and Pipelines
- 42. Combine Functions intoClass Combine Functions into Transform Move Statements into Function Move Statements to Callers Remove Dead Code Rename Field Rename Variable Replace Command with Function New Refactorings Replace Derived Variable with Query Replace Inline Code with Function Call Replace Loop with Pipeline Replace Query with Parameter Replace Subclass with Delegate Return Modified Value Split Phase
- 47.
- 48. My take onthe new book
- 49. Back to theEssence of Refactoring
- 50. Student thesis at TUDresden ""
- 51. Topics 1. What, When,How 2. Benefits 3. Costs / Issues 4. History 5. Catalogue 6. Tools 7. Example
- 52.
- 53. Refactoring (noun): achange made to the internal structure of software to make it easier to understand and cheaper to modify without changing the observable behavior of the software.
- 54. Refactor (verb): torestructure software by applying a series of refactorings without changing the observable behavior of the software.
- 55.
- 56. Code Smells! If itstinks, change it - Grandma Beck
- 57. Mysterious Name Duplicated Code LongFunction Long Parameter List Global Data Mutable Data Divergent Change Shotgun Surgery Feature Envy Data Clumps Primitive Obsession Repeated Switches Code Smells Lazy Element Speculative Generality Temporary Field Message Chains Middle Man Insider Trading Large Class Alternative Classes with Different Interfaces Data Class Refused Bequest Comments Loops
- 58.
- 59.
- 60.
- 61. Code as a CrimeScene Software Design X-Rays Adam Tornhill
- 62.
- 63.
- 64.
- 65. Refactoring is asmuch about safety testing, small steps, commit as it is about code changes.
- 66. Refactoring changes theprograms in small steps. If you make a mistake, it is easy to find the bug.
- 67.
- 68.
- 70. Add Function blog.gdinwiddie.com/2012/12/26/tdd-hat/ 1. Red 2.Green 3. Refactor
- 71. 1. Refactor 2. Green 3.Commit Refactor
- 72. Before you startrefactoring, check that you have a solid suite of tests. These tests must be self-checking. Martin Fowler
- 73. Tests, are yoursafety net Listen to the flight attendent this one time
- 74. Make sure alltests are fully automatic and that they check their own results. Martin Fowler
- 75.
- 76.
- 77. Many small commits Cansquash later
- 78. Run your testsfrequently. Localize tests whenever you compile - every test at least every day. Martin Fowler
- 79. A suite oftests is a powerful bug detector that decapitates the time it takes to find bugs. Martin Fowler
- 80. Unit tests arelike the second pair of eyes of a pair programmer. Kent Beck
- 81.
- 82. Quick Fixes RefactoringRewrite
- 83.
- 84. Continous Clean-Up ● Rename ●Replace comment with function ● Make intent clear ● Intention in your IDE ● Not about polishing
- 85. DRY Three strikes andyou refactor.
- 86. Boy Scout Rule Leaveit better than you found it
- 87. Use >> Reuse Reusewithin your module not across.
- 88.
- 89. ● Before addinga feature ● Addressing technical debt ● Improve testability (seams) ● Improve understandability ● For learning about a new code-base Planned Refactoring
- 90.
- 91.
- 92.
- 93.
- 94. Forces you totest
- 95. Don’t let thefear that testing can’t catch all bugs stop you from writing the tests that will catch most bugs. Martin Fowler
- 96. It is betterto write and run incomplete tests than not to run complete tests. Martin Fowler
- 97. Code Ownership Modify yourcode ownership policies to smooth refactoring.
- 98. Fights Code Rot andDecay
- 99.
- 100.
- 101. APIs Don’t publish interfacesprematurely. Downstream dependencies.
- 102.
- 103. How do Itell my Boss?
- 104.
- 105.
- 106.
- 107. Refactoring & Patterns ●patterns encapsulate good solutions in a context ● represent roles of components ● avoid code-smells ● they can be the goal of a design improvment ● refactorings are steps to those designs
- 108.
- 109. Refactoring Catalogue (myfavorites) Move Function Split Loop Replace Loop with Pipeline (Stream) Replace Magic Literal Replace Derived Variable with Query Replace Typecode with Subclass Replace Superclass with Delegate Replace Control Flag with Break (Return) Introduce Special Case (Null Object) Replace Nested Conditionals with Guad Clauses Extract Function Extract Variable Push Statements into Function Push members up Extract Interface / Superclass Migrate Function Declaration Combine Functions into Transform Encapsulate Collection Replace Temp with Query Separate Query from Modifier Parameterize Function
- 115.
- 116. Tools today makeRefactoring a Joy
- 117. Smart Understanding ofcode & intent Useful suggestions Intentions & Quick fixes
- 118. Use and Learnthe Shortcuts Pragmatic Programmer
- 119.
- 120.
- 121.
- 122. What did you NOTuse yet
- 123.
- 124.
- 125.
- 126. VS Code & VisualStudio
- 127.
- 128. Ask your questions? Thankyou for your time! Follow @mesirii
Editor's Notes
- #10 This is still true today as it was back then.
- #12 best non-fiction book loved the style and the boxes
- #15 It sounds simple and obvious initially but then contains lots of wisdom. And we continually need to teach it.
- #16 It sounds simple and obvious initially but then contains lots of wisdom. And we continually need to teach it.
- #34 basically a refresher update examples chance to a more recent language gather feedback from 20 years accomodate for new refactorings, and not only object oriented
- #36 new motivating example programming language some refactorings were updated / changed / renamed some refactoring were added duplex book https://martinfowler.com/bliki/DuplexBook.html
- #37 Except in Dresden,Germany
- #38 Javascript in 2018 is not that bad anymore (EcmaScript 2016) Simpler Function syntax Classes Testing Widely used -> have to cater for all audiences not just backend-java
- #43 because JavaScript and Java 8
- #50 as usual it is well written and engaging to read lots of common sense, but important to point it out if refactoring is already an part of your workflow you don't need it but hand it to your new colleagues
- #58 I love code smells
- #59 Today you get many of them highlighted by your IDE with intentions Some are obvious some require observation and thinking
- #71 George Dinwiddie
- #77 If your tests run in milliseconds or seconds it's a nobrainer to run them
- #78 If your tests run in milliseconds or seconds it's a nobrainer to run them
- #79 Much easier to roll back a commit than IntelliJ also has "local history" with safepoints
- #90 DRY in your code/module Not across it And not at all costs Inline and re-extract is part of refactoring
- #91 Should be a continous activity
- #92 DRY in your code/module Not across it And not at all costs Inline and re-extract is part of refactoring
- #96 Reason to keep it small Be honest Pull the plug (Lidl) There is always a next day, Software is soft
- #97 depending on the size of the unit if small enough you can throw away, keep the interfaces and redo with lessons learned
- #107 sometimes, seldomly small changes can have big performance impacts - inlining - polymorphic call sites don't need to freak out just be aware and have performance regression tests (git bisect)
- #108 do you tell your management? if they are not onboard? -> change jobs? it's not about polishing
- #124 Find the refactoring (Cmd+P, Shift-Ctrl-A) Remember the shortcut, close the menu use the shortcut