# Code Smell 89 - Math Feature Envy

*One class calculates formulas for another class.*

> TL;DR: Leave the formulas to the objects gathering the information.

# Problems

- Declaratively

- Low reuse

- Real-world concept missing

- Encapsulation

# Solutions

1. Move the math formula to the class

2. Search for [real-world abstractions](https://maximilianocontieri.com/the-one-and-only-software-design-principle)

# Sample Code

## Wrong

[Gist Url]: # (https://gist.github.com/mcsee/4b3483f5be825913df7a6c709efebdbc)
```javascript
function area(rectangle) { 
  return rectangle.width * rectangle.height;
  //Notice we are sending consecutive messages to
  //the same object and doing calculations
}
```

## Right

[Gist Url]: # (https://gist.github.com/mcsee/891b1df84cd9e0528fad2dae42322c54)
```javascript
class Rectangle {
    constructor(width, height, color) { 
         this.height = height;
         this.width = width;
    }
 
    area() {
        return this.width * this.height;
    }
}
```

# Detection

Since many cascading messages are sending to the same object, we can detect a pattern.

# Tags

- Encapsulation

- Coupling

# Conclusion

This is a very basic smell. If we are manipulating another object's characteristics, we should let it do it the maths for us.

# Relations

%[https://maximilianocontieri.com/code-smell-63-feature-envy]

# More Info

- [The one and only one software principle](https://maximilianocontieri.com/the-one-and-only-software-design-principle)

# Credits

Photo by <a href="https://unsplash.com/@michalmatlon">Michal Matlon</a> on <a href="https://unsplash.com/s/photos/math">Unsplash</a>
  
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> Computer science is not about machines, in the same way that astronomy is not about telescopes. There is an essential unity of mathematics and computer science.

_Michael R. Fellows_
 
%[https://maximilianocontieri.com/software-engineering-great-quotes]

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This article is part of the CodeSmell Series.

%[https://maximilianocontieri.com/how-to-find-the-stinky-parts-of-your-code]