# Code Smell 16 - Ripple Effect

*Small changes yield unexpected problems.*

> TL;DR: If small changes have big impact, you need to decouple your system.

# Problems

- Coupling

%[https://maximilianocontieri.com/coupling-the-one-and-only-software-design-problem]

# Solutions

1. Decouple.
2. Cover with tests.
3. Refactor and isolate what is changing.
4. Depend on interfaces.

%[https://maximilianocontieri.com/how-to-decouple-a-legacy-system]

# Examples

- Legacy Systems

# Sample Code

## Wrong

[Gist Url]: # (https://gist.github.com/mcsee/3861429b0a02eb2a3906d0f939cc1809)
```javascript
class Time {
   constructor(hour, minute, seconds) {
     this.hour = hour;    
     this.minute = minute;  
     this.seconds = seconds;  
  }
    now(){
      //call operating system
    }  
}

//Adding a TimeZone will have a big Ripple Effect
//Changing now() to consider timezine will also bring the effect
```

## Right

[Gist Url]: # (https://gist.github.com/mcsee/7fbceedcae6aae7f15d392c9bbe0ffa1)
```javascript
class Time {
   constructor(hour, minute, seconds, timezone) {
     this.hour = hour;    
     this.minute = minute;  
     this.seconds = seconds;  
     this.timezone = timezone;  
  }  
  //Removed now() since is invalid without context
}

class RelativeClock {
   constructor(timezone){
     this.timezone = timezone;
   }
   now(timezone){
     var localSystemTime = this.localSystemTime();
     var localSystemTimezone = this.localSystemTimezone();
     //Do some math translating timezones
     //
     return new Time(..., timezone);     
   }  
}
```

# Detection

- It is not easy to detect problems before they happen. [Mutation Testing](https://en.wikipedia.org/wiki/Mutation_testing) and root cause analysis of [single points of failures](https://en.wikipedia.org/wiki/Single_point_of_failure) may help.

# Tags

- Legacy

# Conclusion

There are multiple strategies to deal with Legacy and coupled systems. We should deal with this problem before it explodes under our eyes.

# Relations

- [Code Smell 08 - Long Chains Of Collaborations](https://maximilianocontieri.com/code-smell-08-long-chains-of-collaborations)

# More info

- [How to Decouple a Legacy System](https://maximilianocontieri.com/how-to-decouple-a-legacy-system)
 
# Credits

Photo by <a href="https://unsplash.com/@jtindall">Jack Tindall</a> on <a href="https://unsplash.com/s/photos/big-wave">Unsplash</a>

* * *

> Architecture is the tension between coupling and cohesion.

_Neal Ford_

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

* * *

This article is part of the CodeSmell Series.

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

*Last update: 2021/06/24*