1 Refactoring
Never be ashamed of making you code better. On the contrary: recognizing code smells in your old code means that you learnt something in the meantime. Only very inexperienced people think that the code they wrote yesterday is perfect.
Refactoring is
- restructuring an existing body of code
- altering its internal structure
- without changing its external behavior wikipedia
We will use tests to ensure that we do not change the external behavior of the code we are refactoring.
A code smell is a piece of bad code that we recognize.
Read the Ruby version of Fowlers refactoring book to learn both code smells and refactorings:
2 Code Smells
This is the list of code smells from Fields, Harvie, Fowler(2010): Refactoring, Ruby Edition. Addison-Wesley. In chapter 6 to 12 of that book they describe refactorings to handle all these problems and more:
- Duplicated Code
- Long Method
- Large Class
- Long Parameter List
- Divergent Change
- Shotgun Surgery
- Feature Envy.
- Data Clumps.
- Primitive Obsession
- Case Statements
- Parallel Inheritance Hierarchies
- Lazy Class.
- Speculative Generality.
- Temporary Field
- Message Chains
- Middle Man
- Inappropriate Intimacy
- Alternative Classes with Different Interfaces.
- Incomplete Library Class
- Data Class
- Refused Bequest
- Comments
- Metaprogramming Madness
- Disjointed API
- Repetitive Boilerplate
3 Tools for Code Quality
Recognizing code that is problematic and should be refactored
is one of the main skills of a developer. Often it is not a
black and white situation: there might be several ways of writing
a certain piece of code, each with it's own pros and cons.
A tool cannot help you make these decision.
But there is a role for tools in this process: especially when faced with a lot of code there are tools that can help you find places you should look at.
A code metric is a quantitive measure of the quality of a piece of code.
The Gem metric_fu combines some metrics. Install it in your
Gemfile, and add a task-file, and run it on the command line metriy_fu.
It will generate a report in tmp/metric_fu/output/.
Saikuro is a good place to start reading the report: it measures cyclomatic complexity, or how deep you nest your control structures.
See Rails Cast no 166 for a more detailed introduction to metric_fu.
Another tool to help find spots where you can improve the quality of
your code is rails_best_practices. Install the gem, but don't put
it in your Gemfile. Just run rails_best_practices -f html in
the main directory of your app. The result will be written to
./rails_best_practices_output.html.
4 Futher Reading
- Fowler, Beck, Brant, Opdyke, Roberts(1999). Refactoring: improving the design of existing code. Addison Wesley. ISBN: 0-201-48567-2.
- Fields, Harvie, Fowler(2010): Refactoring, Ruby Edition. Addison-Wesley.
- codemod a python script