<blockquote>
<p><strong>TL;DR:</strong> Avoid using magic numbers without explanation. Their source is unknown, and we fear changing them.</p>
</blockquote>
<h2 id="heading-problems">Problems</h2>
<ul>
<li><p>Coupling</p>
</li>
<li><p>Low testability</p>
</li>
<li><p>Low readability</p>
</li>
</ul>
<h2 id="heading-solutions">Solutions</h2>
<ul>
<li><p>Rename the constant with a meaningful and intention-revealing name.</p>
</li>
<li><p>Replace constants with parameters, allowing them to be mocked from the outside.</p>
</li>
<li><p>The constant definition should be separate from its usage.</p>
</li>
</ul>
<h2 id="heading-examples">Examples</h2>
<ul>
<li>Algorithms Hyper Parameters</li>
</ul>
<h2 id="heading-sample-code">Sample Code</h2>
<h3 id="heading-wrong">Wrong</h3>
<pre><code class="lang-kotlin"><span class="hljs-function"><span class="hljs-keyword">fun</span> <span class="hljs-title">energy</span><span class="hljs-params">(mass: <span class="hljs-type">Double</span>)</span></span> = (mass * <span class="hljs-number">299792458</span>).pow(<span class="hljs-number">2</span>)
</code></pre>
<h3 id="heading-right">Right</h3>
<pre><code class="lang-kotlin"><span class="hljs-keyword">typealias</span> MetersPerSeconds = <span class="hljs-built_in">Int</span>

<span class="hljs-comment">// Using a specific unit of measure to avoid another code smell</span>
<span class="hljs-keyword">const</span> <span class="hljs-keyword">val</span> LIGHT_SPEED: MetersPerSeconds = <span class="hljs-number">299792458</span>

<span class="hljs-function"><span class="hljs-keyword">fun</span> <span class="hljs-title">energy</span><span class="hljs-params">(mass: <span class="hljs-type">Double</span>)</span></span> = (mass * LIGHT_SPEED).pow(<span class="hljs-number">2</span>)
</code></pre>
<hr />
<p>Stay updated with my latest thoughts and ideas by registering for my <a target="_blank" href="https://yonatankarp.com/newsletter">newsletter</a>. Connect with me on <a target="_blank" href="https://www.linkedin.com/in/yonatankarp/">LinkedIn</a> or <a target="_blank" href="https://twitter.com/yonatan_karp">Twitter</a>. Let's stay connected and keep the conversation going!</p>
<hr />
<h2 id="heading-more-information">More Information</h2>
<ul>
<li><p><a target="_blank" href="https://refactoring.guru/es/replace-magic-number-with-symbolic-constant">Refactoring Guru</a></p>
</li>
<li><p><a target="_blank" href="https://maximilianocontieri.com/how-to-decouple-a-legacy-system">How to Decouple a Legacy System</a></p>
</li>
</ul>
<h2 id="heading-credits">Credits</h2>
<ul>
<li><a target="_blank" href="https://maximilianocontieri.com/code-smell-02-constants-and-magic-numbers">Code Smell 02 - Constants and Magic Numbers</a> by <a class="user-mention" href="https://hashnode.com/@mcsee">Maxi Contieri⭐⭐⭐</a></li>
</ul>


> **TL;DR:** Avoid using magic numbers without explanation. Their source is unknown, and we fear changing them.

## Problems

* Coupling
    
* Low testability
    
* Low readability
    

## Solutions

* Rename the constant with a meaningful and intention-revealing name.
    
* Replace constants with parameters, allowing them to be mocked from the outside.
    
* The constant definition should be separate from its usage.
    

## Examples

* Algorithms Hyper Parameters
    

## Sample Code

### Wrong

```kotlin
fun energy(mass: Double) = (mass * 299792458).pow(2)
```

### Right

```kotlin
typealias MetersPerSeconds = Int

// Using a specific unit of measure to avoid another code smell
const val LIGHT_SPEED: MetersPerSeconds = 299792458

fun energy(mass: Double) = (mass * LIGHT_SPEED).pow(2)
```

---

Stay updated with my latest thoughts and ideas by registering for my [newsletter](https://yonatankarp.com/newsletter). Connect with me on [LinkedIn](https://www.linkedin.com/in/yonatankarp/) or [Twitter](https://twitter.com/yonatan_karp). Let's stay connected and keep the conversation going!

---

## More Information

* [Refactoring Guru](https://refactoring.guru/es/replace-magic-number-with-symbolic-constant)
    
* [How to Decouple a Legacy System](https://maximilianocontieri.com/how-to-decouple-a-legacy-system)
    

## Credits

* [Code Smell 02 - Constants and Magic Numbers](https://maximilianocontieri.com/code-smell-02-constants-and-magic-numbers) by @[Maxi Contieri⭐⭐⭐](@mcsee)

Learn why using constants and magic numbers in Kotlin code can lead to issues. Find solutions to improve code quality and maintainability.

Avoid Constants and Magic Numbers in Kotlin Code

A method makes calculations with many numbers without describing their semantics

Kotlin Code Smell 1 - Constants and Magic Numbers

Problems

Solutions

Examples

Sample Code

Wrong

Right

More Information

Credits

Experienced Senior Software Engineer passionate about functional programming & Kotlin. Excels in app development, optimization, and team collaboration. Let's create something amazing!


A blog with tutorials around spring boot, kotlin  &amp; java languages, and code samples. The blog focuses on, but is not limited to, backend topics in the JVM world

Yonatan Karp-Rudin