Refactoring
and code smells
Martin Osovsky
Y Soft
The outline
* What is good code?
* What is refactoring?
* The importance of testing
* When, why a where to refactor?
* Examples
Important people
* @martinfowler
* @unclebobmartin
* @Bertrand_Meyer
* @ploeh
* @KevlinHenney
* @tastapod
Important books
* Robert C. Martin : Clean Code
* Robert C. Martin : Agile Principles, Patterns, and Practices in C#
* Martin Fowler : Refactoring: Improving the Design of Existing
Code
* Joshua Kerievsky : Refactoring to patterns
* Michael Feathers : Working effectively with Legacy Code
* Garry M. Hall : Adaptive Code via C#
* Gerard Mezsaros : xUnit Test Patterns, Refactoring Test Code
We have already covered…
* 4 Rules of Simple Design
* Unit Testing
SOLID Principles
* Single Responsibility
* Open / Closed
* Liskov Substitution Principle
* Interface Segregation
* Dependency Inversion
Code Smells
1. different abstraction levels (not top down - mixed, skipping
levels, mixing levels in one method)
2. circular dependencies (between classes - mother of all tight
couplings)
3. low cohesion (god classes, script/program wrapped as a class)
4. bad naming (incosistent, non-clear terminology, non-standard
terminology meaningless names, abbreviations, hungarian
notation, pleonasms, FactoryClass, IDisposable, …Exception)
5. Pokemon smell - catch them all, exception abuse
REFACTORING
What is refactoring?
* Controlled change in code that doesn’t change
its external (published) behaviour but improves
internal structure
* Refactoring vs redesign
* Refactoring in the strict sense
When to refactor?
When to refactor?
* When you have the refactoring hat on your head!
* As part of the routine (e.g. TDD)
* After you find weak code (boy scout rule)
* Before you need to introduce code of a new feature (or a
new technology like IoC container)
* Long term planned refactoring
* you need to have a plan and know what is the final
state
When to refactor?
Only when it leads to faster delivery
and better maintenance. Clean
code is means to this end.
Where to refactor?
Where to refactor
* The application same as a building has layers
that have different
* cost of change (outer walls = new building)
* rate of change
* Architecture = the most slow and costly parts of
the system (outer walls, foundations)
How?
* Use IDE all the time (even when renaming!)
* Run tests before and after
* Boundary tests (testing published interfaces)
should stay green
* know most common refactorings (extract …,
rename, move, introduce) - learn to use them as
part of your IDE mastery
And most importantly
Code and discuss your code with
others and learn from the best (github
is full of great code)
Follow the guys form the second slide
Even more importantly
Always code as if the guy who ends up
maintaining your code will be a violent
psychopath who knows where you live.