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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


  • Side effects
  • Biyection Fault
  • Performance issues


  1. Use a short circuit instead of a complete evaluation


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


<?if (isOpen(file) & size(contents(file)) > 0)
// Full evaluation
// Will fail since we cannot retrieve contents
// from not open file


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


[X] Automatic

We can warn our developers when they use full evaluation.


  • Boolean


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

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


Most programming languages support short-circuits.

Many of them have it as the only option.

We need to favor these kinds of expressions.


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



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Maximiliano Contieri

Maximiliano Contieri

I’m a senior software engineer specialized in declarative designs. S.O.L.I.D. and agile methodologies fan.