The Power of Refactoring
Stefan Koopmanschap
PHPCon Italia, Rome, March 19 2009

What will we do?
What is refactoring?
Why refactoring?
When refactoring?
Requirements
HOWTO
2

Stefan Koopmanschap
Who is he?
3

About me
Professional Services Consultant at Ibuildings
10 years of PHP experience
auto didact
married, 2 kids, 6 cats, a bunch of fish
Apple lover
music addict
symfony advocate
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Refactoring
What is it?
5

Refactoring is a disciplined technique for restructuring
an existing body of code, altering its internal structure
without changing its external behavior. Its heart is a
series of small behavior preserving transformations.
Each transformation (called a 'refactoring') does little,
but a sequence of transformations can produce a
significant restructuring. Since each refactoring is small,
it's less likely to go wrong. The system is also kept fully
working after each small refactoring, reducing the
chances that a system can get seriously broken during
the restructuring.
(Martin Fowler - Refactoring.com)
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Code refactoring is the process of changing a computer
program's code to make it amenable to change,
improve its readability, or simplify its structure, while
preserving its existing functionality.
(Wikipedia)
7

What
Code refactoring is the process of changing a computer
program's internal structure without modifying its
external behavior or existing functionality.
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Why
This is usually done to improve code readability, simplify
code structure, change code to adhere to a given
programming paradigm, improve maintainability, or
improve extensibility.
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Improve readability
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Improve maintainability
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Extend/change/implement
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Is it the holy grail?
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Rewrite
A rewrite in computer programming is the act or result of
re-implementing a large portion of existing functionality
without re-use of its source code. When the rewrite is not
using existing code at all, it is common to speak of a
rewrite from scratch. When instead only parts are re-
engineered, which have otherwise become complicated to
handle or extend, then it is more precise to speak of code
refactoring.
(Wikipedia)
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Refactor vs Rewrite
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Refactor vs Rewrite
Refactor whenever it is possible
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Refactor vs Rewrite
Refactor whenever it is possible
Big change? Try to cut it into smaller units
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Refactor vs Rewrite
Refactor whenever it is possible
Big change? Try to cut it into smaller units
Still have to break the API? Go ahead, and rewrite!
15

Refactor vs Rewrite
Refactor whenever it is possible
Big change? Try to cut it into smaller units
Still have to break the API? Go ahead, and rewrite!
Don’t take the decision in 5 minutes
15

Refactor vs Rewrite
Refactoring takes less effort
Nice for you
Better for the quality of your work
Breaking the API is more work
Ensure all calling code is altered as well
Update your unit tests
Update your documentation
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Requirements
for successful refactoring
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Requirements
Codebase knowledge
Structured API
Unit testing
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Codebase knowledge
Know what to change quickly
Be aware of your changes
Be aware of impact of your changes on other components
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Structured API
Refactoring DOES NOT REPLACE design!
You need a good API that allows internal changes
Additions to existing API’s should not change existing API
Keep small “units”
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Unit testing
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Unit testing
Unit testing is your first point of QA
They safeguard you from unexpected side effects
Test - Change - Test
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When?
Timing of refactoring
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Two moments of refactoring
Big chunks
Continuous refactoring
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Big Chunks
As you encounter problems, you keep track
• Ticketing system
• TODO list
• Inline comments
Schedule one or more moments in your project
• Work through your list
• Refactor them
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Big Chunks work?
Advantages
• Set times for refactoring
• Focus on your project when you need to
• Works well for functional changes
Disadvantages
• Refactoring gets cancelled first with tight deadlines
• You may have forgotten specific solutions already
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Continuous Refactoring
Refactor while you work
Encounter a problem, fix it!
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Continuous Refactoring works?
Advantages
• No need to schedule seperate time
• Continuous improvement of your code
Disadvantages
• Danger of losing the balance between tasks and refactoring
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Who should refactor?
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Who should refactor?
Someone with knowledge of the codebase
• Or at least the part that is being refactored
Not necessarily the code owner
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An example
user authentication
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A test-driven approach
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My first implementation
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My first implementation
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A more dynamic version
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A more dynamic version
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Tips and tricks
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Some tips and tricks
Write unit tests before you start refactoring
Code documentation (phpDoc) is your friend
Don’t trust your IDE’s refactoring options
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Looking back
What is refactoring?
Why do we want to refactor?
Is it the holy grail?
Refactoring vs Rewriting
Requirements
How to do it
Tips and tricks
37

The Power of Refactoring
38

Creative Commons Rocks!
Readability:
http://www.flickr.com/photos/vipulmathur/
471634239/ (by-nc-sa/2.0)
Maintainability:
http://www.flickr.com/photos/comicbase/
2117680144/ (by-nc-sa/2.0)
Extend:
http://www.flickr.com/photos/auntiep/
221951988/ (by-nc-sa/2.0)
Holy Grail:
http://www.flickr.com/photos/joebeone/
153921142/ (by/2.0)
Würst test ever:
http://www.flickr.com/photos/pingles/
1341229619/ (by-nc-nd/2.0)
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Questions ?
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Thank you!
Contact details:
Stefan Koopmanschap
http://www.leftontheweb.com/
http://www.ibuildings.com/
http://www.twitter.com/skoop
http://www.slideshare.net/skoop
http://joind.in/talk/view/240