Refactoring Rails

This guide will show you how to refactor your code.

By referring to this guide, you will be able to:

  • Get to know some tools that help you find problematic aspects of your code
  • Learn general refactoring practice from concrete examples

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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:

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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
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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.

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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.
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