# 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

# Sample Code

## Wrong

``````function area(rectangle) {
return rectangle.width * rectangle.height;
//Notice we are sending consecutive messages to
//the same object and doing calculations
}
``````

## Right

``````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.

# Credits

Photo by Michal Matlon on Unsplash

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