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Cover image for Code Smell 158 - Variables not Variable
Maxi Contieri
Maxi Contieri

Posted on • Originally published at

Code Smell 158 - Variables not Variable

You assign a value to a variable and use it, but never change it

TL;DR: Be declarative on mutability.


  • Readability

  • Honor the Bijection mutability.

  • Potential performance and memory issues.


  1. Change the variable to a constant and be clear on its scope


We are always learning from the domain.

Sometimes we guess that a value can change with the MAPPER.

Later on, we learn it won't change.

Therefore we need to promote it to a constant.

This will also avoid Magic Constants

Sample Code



function configureUser() {
  $password = '123456';
  // Setting a password on a variable is another vulnerability
  // And Code Smell
  $user = new User($password);
  // Notice Variable doesn't change
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define("USER_PASSWORD", '123456')

function configureUser() {  
  $user = new User(USER_PASSWORD);

// or 

function configureUser() {  
  $user = new User(userPassword());

function userPassword() : string {
  return '123456';

// Case is oversimplification as usual
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[X] Automatic

Many linters check if the variable has just one assignment.

We can also perform mutation testing and try to modify the variable to see if tests break.


  • Mutability


We must challenge ourselves and refactor when the variable scope is clear and we learn more about its properties and mutability.



More Info


Code Smells are just my opinion.


Photo by Noah Buscher on Unsplash

A complex system that works is invariably found to have evolved from a simple system that worked.

John Gall

This article is part of the CodeSmell Series.

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