Presented at DevReach 2013. As developers, most of our time is spent working on existing software. Sure, occasionally we get the chance to fire up a new Solution in Visual Studio, and that can be exciting. But after the first day, we find ourselves once more having to deal with the work we did yesterday. And today, we know more than we did yesterday, so there are things we’d do differently, if we had it to do over. Over time, software rots. If we’re not diligent, our beautiful code can degrade into a worthless mess. Keeping our code in working condition is no different than changing the oil in our car – it’s preventive maintenance. In this session, Steve will look at some common places to look for signs of degradation in existing applications, and steps to take to improve the code. Examples will use C# and primarily ASP.NET.

1. Improving the Quality of
Existing Software
Steve Smith
Telerik
ardalis.com @ardalis

2. Software Rots

4. Technical Debt
• Low quality code and
shortcuts in our
applications
• Technical debt, like real
debt, has direct cost and
interest

5. http://www.jimhighsmith.com/

6. Preventive Maintenance
• Refactoring
– Eliminate Duplication
– Simplify Design
• Automated Tests
– Verify correctness
– Avoid regressions
– Increase Confidence

7. When should you refactor?
• While delivering value

9. Refactoring Should Not Change
System Behavior

10. Refactoring Process
• Verify existing behavior
• Write Characterization Tests if none exist
– Find test points
– Break dependencies
• Apply Refactoring
• Confirm existing behavior is preserved

11. Characterization Tests
Process
1. Write a test 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 pass

14. S O L I DPrinciples
http://flickr.com/photos/kevinkemmerer/2772526725

15. Principles of OO Design
0. Don’t Repeat Yourself (DRY)
1. Single Responsibility
2. Open/Closed
3. Liskov Substitution
4. Interface Segregation
5. Dependency Inversion

17. Don’t Repeat
Repeat Yourself
• Duplication in logic calls for abstraction
• Duplication in process calls for
automation

18. Common Refactorings
• Replace Magic Number/String
• Parameterize Method
• Pull Up Field
• Pull Up Method
• Replace Conditional With Polymorphism
• Introduce Method

19. 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
}

21. Single Responsibility Principle
The Single 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

22. Example Responsibilities
• Persistence
• Validation
• Notification
• Error Handling
• Logging
• Class Selection / Construction
• Formatting
• Parsing
• Mapping

23. Dependency and Coupling
• Excessive coupling makes changing
legacy software difficult
• Breaking apart responsibilities and
dependencies is a large part of working
with existing code

24. Common Refactorings
• Extract Class
• Extract Method
• Move Method

25. Heuristics and Code Smells
• Visual Studio Metrics

26. Code Smell: Regions
More on Regions: http://ardalis.com/regional-differences

28. Open / Closed Principle
The Open / Closed Principle states that software entities
(classes, modules, functions, etc.) should be open for
extension, but closed for modification.
Wikipedia

29. Open / Closed Principle
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, Object Oriented Software Construction

30. Common Refactorings
• Extract Interface / Apply Strategy Pattern
• Parameterize Method
• Form Template Method

31. OCP Fail

32. OCP OK

33. OCP Fail
public bool IsSpecialCustomer(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;
}

34. 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;
}

36. Liskov Substitution Principle
The Liskov 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.

37. Common Refactorings
• Collapse Hierarchy
• Pull Up / Push Down Field
• Pull Up / Push Down Method

38. Liskov Substitution Fail
foreach(var employee in employees)
{
if(employee is Manager)
{
Helpers.PrintManager(employee as Manager);
break;
}
Helpers.PrintEmployee(employee);
}

39. Liskov Substitution OK
foreach(var employee in employees)
{
employee.Print();
// or
Helpers.PrintEmployee(employee);
}

41. Interface Segregation Principle
The Interface 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

42. Common Refactorings
• Extract Interface

43. Keep Interfaces Small and
Focused

44. Membership Provider

45. ISP Fail (sometimes)
public IRepository<T>
{
T GetById(int id);
IEnumerable<T> List();
void Create(T item);
void Update(T item);
void Delete(T item);
}

46. ISP OK (for CQRS for example)
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);
}

48. Dependency Inversion Principle
High-level modules 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#

49. Dependency Inversion Principle
• Depend on Abstractions
– Interfaces, not concrete types
• Inject Dependencies into Classes
• Structure Solution so Dependencies Flow
Toward Core
– Onion Architecture (a.k.a. Ports and Adapters)

50. Application Layers

51. Data Access Evolution
No separation 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

52. 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

53. 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

54. DIP Architecture (aka Ports and
Adapters)

55. 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

56. Common Refactorings
• Extract Class
• Extract Interface / Apply Strategy Pattern
• Extract Method
• Introduce Service Locator / Container

57. DIP Fail

58. Some Improvement (Façade)

59. DIP OK (Strategy)

60. DIP OK (Strategy)

61. 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?

62. 0
2
4
6
8
10
12
14
16
Week 1 Week 2 Week 3 Week 4 Week 5 Week 6 Week 7 Week 8 Week 9
User Stories Completed
High Quality Low Quality Column1

63. 0
2
4
6
8
10
12
14
16
18
20
Week 1 Week 2 Week 3 Week 4 Week 5 Week 6 Week 7 Week 8 Week 9
User Stories Completed
High Quality Low Quality Column1

64. Summary
• Maintain / Improve Application Code
• Follow DRY/SOLID Principles
• Use Characterization Tests to “fix”
behavior
• Apply Common Refactorings
• Re-run Tests After (and during)
Refactorings
• Train and Practice to Write Better Code
Faster

65. References
http://bit.ly/SFkpmq
 Refactoring Catalog
 http://www.refactoring.com/catalog/index.html
 Onion Architecture
 http://jeffreypalermo.com/blog/the-onion-architecture-part-1/

66. 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

67. Thank you!
@ardalis
ardalis.com
http://facebook.com/stevenandrewsmith