Code Smell 86 - Mutable Const Arrays

Code Smell 86 - Mutable Const Arrays

Maxi Contieri
·Aug 25, 2021·

1 min read

Subscribe to my newsletter and never miss my upcoming articles

Listen to this article

Const declares something to be constant. Can it mutate?

TL;DR: Don't rely on languages cheating about directives.

Problems

  • Unexpected side effects

  • Accidental complexity

Solutions

  1. Use better languages.

  2. Use spread operator.

Sample Code

Wrong

const array = [1, 2];

array.push(3)

//array => [1, 2, 3]
//Wasn't it constant ?
//constant != immutable ?
const array = [1, 2];

const newArray = [...array,3 ]

//array => [1, 2] Didn't mutate
//newArray = [1, 2, 3]

Detection

Since this is a "language feature", we can explicitly forbid it.

Tags

  • Mutability

  • JavaScript

Conclusion

We should always favour immutability on our designs and take extra care with side effects.

More Info

Credits

Photo by Zorik D on Unsplash

Thank you, Oliver Jumpertz for this tip.


Correctness is clearly the prime quality. If a system does not do what it is supposed to do, then everything else about it matters little.

Bertrand Meyer


This article is part of the CodeSmell Series.

 
Share this

Impressum

Technical Opinions are my own. I don't have the revealed truth.

Software Design is a creative activity. These are hints and not rigid rules.

I write on BackEnd Business Systems and OOP Design. My advice/experience might not suit other systems.