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Cover image for Code Smell 02 - Constants and Magic Numbers

Code Smell 02 - Constants and Magic Numbers

Maxi Contieri
Learn something new every day. - I am a senior software engineer working in industry, teaching and writing on software design, SOLID principles, DDD and TDD.
Originally published at maximilianocontieri.com Updated on ・1 min read

A method makes calculations with lots of numbers without describing their semantics.

TL;DR: Avoid Magic numbers without explanation. We don't know their source and we are very afraid of changing then.

Problems

  • Coupling
  • Low testability
  • Low readability

Solutions

1) Rename the constant with a semantic and name (meaningful and intention revealing).

2) Replace constants with parameters, so you can mock them from outside.

3) The constant definition is often a different object than the constant (ab)user.

Examples

  • Algorithms Hyper Parameters

Sample Code

Wrong

<?

function energy($mass) {

    return $mass * (300000 ^ 2);
}
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Right

<?

function energy($mass) {

    return $mass * (LIGHT_SPEED_KILOMETERS_OVER_SECONDS ^ 2);
}
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Detection

Many linters can detect number literal in attributes and methods.

Tags

  • Hard coded
  • Constants

More info

Credits

Photo by Kristopher Roller on Unsplash


In a purely functional program, the value of a [constant] never changes, and yet, it changes all the time! A paradox!

Joel Spolsky


This article is part of the CodeSmell Series.

Last update: 2021/05/31

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