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Improving the Quality of Existing Software
The document provides strategies for improving the quality of existing software through refactoring and adhering to SOLID principles, emphasizing the importance of reducing technical debt. It outlines various common refactorings, test practices, and the significance of maintaining clear dependencies within software design. The aim is to promote better coding practices and foster an environment of continuous improvement in software development.
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Improving the Quality of Existing Software
- 1. Improving the Qualityof Existing Software Steve Smith Falafel Software @ardalis | ardalis.com
- 2. Tweet Away • LiveTweetingand Photos are encouraged • Questions and Feedback are welcome • Use #DevIntersection and/or #ImproveSoftware • Or #DevIntersectionImprovingTheQualityOfExistingSoftware
- 3. Pluralsight I have some1-month free passes; see me after if you’d like one
- 4.
- 6. Technical Debt • Lowquality code and shortcuts in our applications • Technical debt, like real debt, has direct cost to pay off as well as interest
- 7.
- 8. Preventive Maintenance • Refactoring •Eliminate Duplication • Simplify Design • AutomatedTests • Verify correctness • Avoid regressions • Increase Confidence
- 9. When should yourefactor? • While delivering value
- 10. “ ” You don’t needpermission to practice basic hygiene when you write software. http://ardalis.com/when-should-you-refactor/ Make cleaning up your code something you do as part of writing code.
- 12. Refactoring Should NotChange System Behavior
- 13. Refactoring Process • Verifyexisting behavior • Write CharacterizationTests if none exist • Find test points • Break dependencies • Apply Refactoring • Confirm existing behavior is preserved
- 14. CharacterizationTests Process 1. Write atest you know will fail 2. Use the output of the failing test to determine the existing behavior to assert 3. Update the test with the new value/behavior 4. Run the test again – it should now pass
- 17. S O LI DPrinciples http://flickr.com/photos/kevinkemmerer/2772526725/
- 18. Principles of OODesign 0. Don’t RepeatYourself (DRY) 1. Single Responsibility 2. Open/Closed 3. Liskov Substitution 4. Interface Segregation 5. Dependency Inversion
- 20. Don’t Repeat RepeatYourself • Duplicationin logic calls for abstraction • Duplication in process calls for automation
- 21. Common Refactorings • ReplaceMagic Number/String • Parameterize Method • Pull Up Field • Pull Up Method • Replace Conditional With Polymorphism • Introduce Method
- 22. Common Source ofRepetition: Role Checks if(user.IsInRole(“Admins”) { // allow access to resource } // favor privileges over role checks // ardalis.com/Favor-Privileges-over-Role-Checks var priv = new ContentPrivilege(user, article); if(priv.CanEdit()) { // allow access }
- 23. Visual Studio CodeClones • Find similar blocks of code in your projects/solution • Can detect matches that are similar but vary in small ways (like variable names) • Available inVS2015 Premium and Ultimate
- 25. Single Responsibility Principle TheSingle Responsibility Principle states that every object should have a single responsibility, and that responsibility should be entirely encapsulated by the class. Wikipedia There should never be more than one reason for a class to change. Robert C. “Uncle Bob” Martin
- 26. What is aresponsibility? “My CustomerManager class is only responsible for anything to do with a Customer.That follows SRP, right?”
- 27. Examples of Responsibilities •Persistence • Validation • Notification • Error Handling • Logging • Class Selection / Construction • Formatting • Parsing • Mapping
- 28. Dependency and Coupling •Excessive coupling makes changing legacy software difficult • Breaking apart responsibilities and dependencies is a large part of working with existing code
- 29. Common Refactorings • ExtractClass • Extract Method • Move Method
- 30. Heuristics and CodeSmells • Visual Studio Metrics
- 31.
- 33. Code Smell: Regions Moreon Regions: http://ardalis.com/regional-differences
- 35. Open / ClosedPrinciple The Open / Closed Principle states that software entities (classes, modules, functions, etc.) should be open for extension, but closed for modification. Wikipedia
- 36. Open / ClosedPrinciple Open to Extension New behavior can be added in the future Closed to Modification Changes to source or binary code are not required Dr. Bertrand Meyer originated the OCP term in his 1988 book, ObjectOrientedSoftwareConstruction
- 37. Common Refactorings • ExtractInterface / Apply Strategy Pattern • Parameterize Method • FormTemplate Method
- 38.
- 39.
- 40. OCP Fail public boolIsSpecialCustomer(Customer c) { if(c.Country == “US” && c.Balance < 50) return false; if(c.Country == “DE” && c.Balance < 25) return false; if(c.Country == “UK” && c.Balance < 35) return false; if(c.Country == “FR” && c.Balance < 27) return false; if(c.Country == “BG” && c.Balance < 29) return false; if(c.Age < 18 || c.Age > 65) return false; if(c.Income < 50000 && c.Age < 30) return false; return true; }
- 41. OCP OK private IEnumerable<ICustomerRule>_rules; public bool IsSpecialCustomer(Customer c) { foreach(var rule in _rules) { if(rule.Evaluate(c) == false) return false; } return true; }
- 43. Liskov Substitution Principle TheLiskov Substitution Principle states that Subtypes must be substitutable for their base types. Agile Principles, Patterns, and Practices in C# Named for Barbara Liskov, who first described the principle in 1988.
- 44. Common Refactorings • CollapseHierarchy • Pull Up / Push Down Field • Pull Up / Push Down Method
- 45. Liskov Substitution Fail foreach(varemployee in employees) { if(employee is Manager) { Helpers.PrintManager(employee as Manager); break; } Helpers.PrintEmployee(employee); }
- 46. Liskov Substitution OK foreach(varemployee in employees) { employee.Print(); // or Helpers.PrintEmployee(employee); }
- 47. Nulls Break Polymorphism foreach(varemployee in employees) { if(employee == null) { // print not found message break; } Helpers.PrintEmployee(employee); } http://ardalis.com/nulls-break-polymorphism
- 49. Interface Segregation Principle TheInterface Segregation Principle states that Clients should not be forced to depend on methods they do not use. Agile Principles, Patterns, and Practices in C# Corollary: Prefer small, cohesive interfaces to “fat” interfaces
- 50. Common Refactorings • ExtractInterface
- 51. Keep Interfaces Smalland Focused
- 52.
- 53. ISP Fail (sometimes) publicIRepository<T> { T GetById(int id); IEnumerable<T> List(); void Create(T item); void Update(T item); void Delete(T item); }
- 54. ISP OK (i.e.to support CQRS) public IRepository<T> : IReadRepository<T>, IWriteRepository<T> { } public IReadRepository<T> { T GetById(int id); IEnumerable<T> List(); } public IWriteRepository<T> void Create(T item); void Update(T item); void Delete(T item); } Existing implementations of IRepository<T> are unaffected by pulling out smaller interfaces!
- 56. Dependency Inversion Principle High-levelmodules should not depend on low-level modules. Both should depend on abstractions. Abstractions should not depend on details. Details should depend on abstractions. Agile Principles, Patterns, and Practices in C#
- 57. Dependency Inversion Principle •Depend on Abstractions • Interfaces, not concrete types • Inject Dependencies into Classes • Structure Solution so Dependencies FlowToward Core • Onion Architecture (a.k.a. Ports and Adapters, a.k.a. Hexagonal Architecture)
- 58.
- 59. Data Access Evolution Noseparation of concerns: Data access logic baked directly into UI ASP.NET Data Source Controls Classic ASP scripts Data access logic in UI layer via codebehind ASP.NET Page_Load event ASP.NET Button_Click event User Interface Database Compile Time Runtime
- 60. Data Access :Helper Classes Calls to data made through a utility Example: Data Access Application Block (SqlHelper) Logic may still live in UI layer Or a Business Logic Layer may make calls to a Data Access Layer which might then call the helper User Interface Database Compile Time Runtime Helper Class
- 61. What’s Missing? Abstraction! No way to abstract away data access Tight coupling Leads to Big Ball of Mud system Solution: Depend on interfaces, not concrete implementations What should we call such interfaces? Repositories! User Interface Database Compile Time Runtime Core IFooRepository Infrastructure SqlFooRepository
- 62. DIP Architecture (akaPorts and Adapters)
- 63. Common Dependencies • Framework •Third Party Libraries • Database • File System • Email • Web Services • System Resources (Clock) • Configuration • The new Keyword • Static methods • Thread.Sleep • Random See also responsibilities: • Persistence • Validation • Notification • Error Handling • Logging • Class Selection / Construction • Formatting • Parsing • Mapping
- 64. Common Refactorings • ExtractClass • Extract Interface / Apply Strategy Pattern • Extract Method • Introduce Service Locator / Container
- 65.
- 66. Hidden Dependencies • CheckoutDepends on an available SMTP server, but the class doesn’t reflect this • Follow the Explicit Dependencies Principle • http://deviq.com/explicit-dependencies-principle/
- 67.
- 68. DIP OK (StrategyPattern / DI)
- 69. DIP OK (StrategyPattern / DI)
- 70. Self-Improvement and Quality •How fast can you produce: • Code you believe to be of high quality • Code that maybe gets the job done, but you believe to be of low quality • Which one can you produce more quickly? • Why? • How can we develop our skills and our tools so that building quality is natural and easier than not doing so?
- 71. 0 2 4 6 8 10 12 14 16 Week 1 Week2 Week 3 Week 4 Week 5 Week 6 Week 7 Week 8 Week 9 User Stories Completed High Quality Low Quality
- 72. 0 2 4 6 8 10 12 14 16 18 20 Week 1 Week2 Week 3 Week 4 Week 5 Week 6 Week 7 Week 8 Week 9 User Stories Completed High Quality Low Quality
- 73. Summary •Maintain / ImproveApplicationCode •Follow DRY/SOLID Principles •Use CharacterizationTests to “fix” behavior •Apply Common Refactorings •Re-runTests After (and during) Refactorings •Be ExplicitAbout Class Dependencies •Train and Practice to Write Better Code Faster
- 74. Learn More • DevIQ.com–Take Pride inYour Code • Ardalis.com • @ardalis • Pluralsight: • SOLID Principles of OO Design • N-TierArchitecture in C# • Refactoring Fundamentals • Domain-Driven Design Fundamentals • Design Pattern Library
- 75. Books Refactoring http://amzn.to/110tscA Refactoring to Patterns http://amzn.to/Vq5Rj2 Working Effectively with Legacy Code http://amzn.to/VFFYbn Code Complete http://amzn.to/Vq5YLv Clean Code http://amzn.to/YjUDI0
Editor's Notes
- #3 https://twitter.com/hashtag/devintersection https://twitter.com/hashtag/breakdependencies
- #5 How? Duplication Excess Coupling Quick Fixes Hacks
- #6 Over time, neglect can turn software from well-oiled machinery into heaps of useless junk.
- #7 Typically the low quality code was left because of the need to meet deadlines, but once in place, the justification for having put it there no longer matters. Whenever you are forced to work around the hacks, bad code, etc, in your application, the decrease in your productivity represents interest on technical debt. If you spend time refactoring the code to improve its quality, you are paying down the principal of the technical debt (and thus reducing future interest costs).
- #10 Should we spend an iteration or a month just trying to improve the quality of the system, and pay down technical debt? What would you think if you went to your favorite restaurant, only to find that it was closed for a month, with a sign explaining that it needed to clean up things that had gotten out of hand due to neglect. Would you feel as confident about eating the product of that kitchen, knowing it had let things go so wrong that it now needed a month without producing food just to clean up the mess it had created. How do you think our customers should feel if we request time to clean up our code instead of fixing bugs or delivering new features?
- #13 By definition, refactoring attempts to improve the quality of a software application without changing its behavior. If you’re changing behavior, you’re not refactoring, you’re fixing a bug or adding a feature (hopefully – or adding a bug).
- #14 Only refactor code while your tests are passing. Make sure they still pass when you are done. Break large refactorings into small steps and test after each step.
- #15 Note that characterization tests, though they should be automated, are often not what we would think of as unit tests, or perhaps even integration tests. For instance, you could dump a log file showing the relevant state of the application, and then use that as the basis for your characterization test by comparing against it after your changes.
- #16 Avoid creating a big ball of mud system, where tracing through your code and its dependencies is like trying to unwind a tangled mess of spaghetti.
- #17 Water break
- #19 Principles provide guidance for refactoring. They provide a consistent target to aim toward.
- #23 A very common source of repetition of code is role checks. These often describe different scenarios in different circumstances. For instance, maybe administrators can do anything, but managers can access resources within their division, etc. Encapsulating the logic of CanView, CanCreate, CanEdit, etc. in privilege objects makes these rules explicit, easier to test, and gives them a single location to live in the application.
- #31 Visual Studio can quickly analyze a project and show statistics for the classes and methods in the project. The maintainability index, cyclomatic complexity, and lines of code are all great metrics to pay attention to. The ideal maintainability index is 100, but don’t expect to hit that with any code that’s doing real work. However, you should certainly able to keep it above 50. Demo GildedRose.
- #33 Using Excel
- #34 I’m not a fan of regions. They mainly exist because at one time they were a reasonable means of hiding generated code, before we had support for partial classes and other language features to deal with this. The worst offense with regions is when they’re used within a method, like this: (click) They’re also bad when used at the class level for “standard” formatting of code, making it impossible to actually see what the code does, like this: (click) Can someone tell me what this class does? (click) I have a whole article devoted to why using regions is a bad habit, anti-pattern, code smell, whatever you prefer. It includes some survey results on the most common ways people use them as well. (click)
- #35 Open-Closed Principle
- #37 Software can only be open to extension in a few different axes, and each additional bit of flexibility adds complexity to the software. Thus, this flexibility should be added only when needed, not simply anticipated.
- #41 What happens when we need to add another country? What happens when we must add another rule? How can we refactor this so this method no longer needs to change?
- #42 Define a type to describe a rule. Move each rule into its own type. Create a collection of rules to apply and apply them. Pass the set of rules into the IsSpecialCustomer() method’s class (or even the method itself).
- #46 Any time you find that you need to check the type of an object within a polymorphic block of code (such as a foreach), this is a sign that you are breaking LSP.
- #48 Nulls break polymorphism and violate LSP just as much as other subtypes that aren’t substitutable! Try to avoid the possibility of dealing with nulls in polymorphic code like foreach loops – consider using Null Object Pattern to address.
- #54 This is an extemely common example of the Repository design pattern. In fact, I use this exact pattern in quite a few production applications today. There’s nothing inherently wrong with this implementation on its own. However, sometimes it does violate ISP if you need to separate Commands from Queries
- #55 You can create small interfaces and compose the larger interfaces from the smaller ones if you control all of the code and you can’t simply do away with the larger interfaces. In this case, the separation of interfaces would allow us to do something like implement caching only on the read operations, and implement delayed writes using some kind of queue or message bus for the write operations.
- #59 “Legacy” N-Tier Logical Architecture
- #66 Hidden Dependencies
- #69 Extract interface Implement interface with tightly coupled original code
- #70 Mention Explicit Dependencies Principle
- #71 Get them excited.