1. Metric Driven Refactoring

2. Metrics
• The Bad
• The Good
• The Compromise

3. The Bad
• Often misleading
• Often misunderstood
• Lines of Code
• Number of Defects
• Turn time

4. The Good
• Can add objectivity to a
subjective exercise
• Can help us focus on
problem areas
• Can provide guidance at
an early stage

5. The Compromise
• Metrics must be easily
understood
• Metrics must provide
actionable data
• Metric must be easy to
calculate

6. What is Refactoring
• Small incremental
changes
• Changes the internal
structure
• Does not change the
external behavior

7. Why Refactor
• Improve maintainability
• Improve performance
• Improve legibility
• Make code reusable
• Pay off design deficit

8. Code Smells
• Indicate that something
maybe wrong with code
• Smells point to the
need to refactor
• Individual smells are
often associated with
specific refactors

9. Sample Code Smells
• Long method
• Feature Envy
• Switch Statement Smell
• Shot Gun Surgery
• Large Class
• Comments

10. Smelly Metrics
• Metrics that Help
identify Code in need of
Refactoring
• Metric provides discrete
values that can be
compared against
guidelines

11. Instruction Count
• Number of IL
Instructions in a
Method
• More instructions =
Longer Method
• More Instructions =
Less Focused Method
• More Instructions =
More Effort to Support

12. Cyclomatic Complexity
• Number of Logical Paths
Through a Method
• Number of Test Cases
Needed for Full
Coverage
• Higher Complexity =
More Difficult to
Support
• Higher Complexity =
More likely to Have
Errors

13. Guidelines
• Guidelines – Not Hard
and Fast Rules
• Exceptions Allowed but
Must be Understood
• 200 Instructions per
Method or Less
• Cyclomatic Complexity
below 10
• Cyclomatic Complexity
= 1 in a View

14. Running Metrics

15. Common Refactors
• Extract Method
• Replace Method with
Method Object
• Decompose Conditional

16. Apply Some Refactors

17. New Best Practices
• Review Metrics Before
and After Each Round of
Code Changes
• “Do No Harm”
• Improve the Methods
that You Touch
• Adhering to these
Guidelines will Create
Better Software

18. Where to Get More Information
• http://www.geekswithb
logs.net/nharrison
• http://www.simple-
talk.com/author/nick-
harrison/
• http://www.refactoring.
com/catalog/index.html
• http://www.red-
gate.com/products/refl
ector/index.htm