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Code Smell 140 - Short Circuit Evaluation

Code Smell 140 - Short Circuit Evaluation

We learn short circuits in our first programming courses. We need to remember why.

TL;DR: Be lazy when evaluating boolean conditions

Problems

  • Side effects

  • Bijection Fault

  • Performance issues

Solutions

  1. Use a short circuit instead of a complete evaluation

Context

We learn booleans in our 101 computer courses.

Boolean's truth tables are great for mathematics, but we need to be more intelligent as software engineerings.

Short circuit evaluation helps us to be lazy and even build invalid full evaluations.

Sample Code

Wrong

<?

if (isOpen(file) & size(contents(file)) > 0)
  // It performs a full evaluation since it is the bitwise AND
  // will fail since you cannot retrieve contents
  // from a file that is not open

Right

<?

if (isOpen(file) && size(contents(file)) > 0)
  // Short circuit evaluation 
  // If the file is not open it willtry to get the contents

Detection

[X] Automatic

We can warn our developers when they use full evaluation.

Exceptions

Don't use short-circuit as an IF alternative.

if the operands have side effects, this is another code smell.

Tags

  • Boolean

Conclusion

Most programming languages support short-circuits.

Many of them have it as the only option.

We need to favor these kinds of expressions.

Relations

Code Smell 101 - Comparison Against Booleans

Code Smell 69 - Big Bang (JavaScript Ridiculous Castings)

Code Smell 145 - Short Circuit Hack

More Info

Writing a class without its contract would be similar to producing an engineering component (electrical circuit, VLSI (Very Large Scale Integration) chip, bridge, engine...) without a spec. No professional engineer would even consider the idea.

Bertrand Meyer

Software Engineering Great Quotes

This article is part of the CodeSmell Series.

How to Find the Stinky Parts of your Code