<blockquote>
<p><strong>TL;DR:</strong> Avoid Magic numbers without explanation. We don't know their source and are afraid to change them.</p>
</blockquote>
<h1 id="heading-problems">Problems</h1>
<ul>
<li><p>Coupling</p>
</li>
<li><p>Low testability</p>
</li>
<li><p>Low readability</p>
</li>
</ul>
<h1 id="heading-solutions">Solutions</h1>
<ul>
<li><p>Rename the constant with a semantic and name (meaningful and intention-revealing).</p>
</li>
<li><p>Replace constants with parameters, so you can mock them from the outside.</p>
</li>
<li><p>A constant definition is often a different object than the constant (ab)user.</p>
</li>
</ul>
<h1 id="heading-examples">Examples</h1>
<ul>
<li>Algorithms Hyper Parameters</li>
</ul>
<h1 id="heading-sample-code">Sample Code</h1>
<h2 id="heading-wrong">Wrong</h2>
<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>
<h2 id="heading-right">Right</h2>
<pre><code class="lang-kotlin"><span class="hljs-keyword">typealias</span> MetersPerSeconds = <span class="hljs-built_in">Int</span>

<span class="hljs-comment">// We're using here the specific unit of measure to avoid yet 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>
<h1 id="heading-more-information">More Information</h1>
<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>
<h1 id="heading-credits">Credits</h1>
<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 Magic numbers without explanation. We don't know their source and are afraid to change them.

# Problems

*   Coupling
    
*   Low testability
    
*   Low readability
    

# Solutions

*   Rename the constant with a semantic and name (meaningful and intention-revealing).
    
*   Replace constants with parameters, so you can mock them from the outside.
    
*   A constant definition is often a different object than the constant (ab)user.
    

# Examples

*   Algorithms Hyper Parameters
    

# Sample Code

## Wrong

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

## Right

```kotlin
typealias MetersPerSeconds = Int

// We're using here the specific unit of measure to avoid yet another code smell
const val LIGHT_SPEED: MetersPerSeconds = 299792458

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

# 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)

A method makes calculations with many numbers without describing their semantics

Kotlin Code Smell 001 - Constants and Magic Numbers

Problems

Solutions

Examples

Sample Code

Wrong

Right

More Information

Credits

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 | kotlin for backend developer skills | java for backend developer skills | SpringBoot | Tutorials

Yonatan Karp-Rudin