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.

Relations

More Info

• The one and only one software principle

Credits

Photo by Michal Matlon on Unsplash

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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

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This article is part of the CodeSmell Series.