Code Smell 36 - Switch/case/elseif/else/if statements

First programming lesson: Control structures. Senior developer lesson: avoid them.

TL;DR: Don use Ifs or its friends

Problems

Too many decisions together
Coupling
Duplicated code
Violation of Open/Closed Principle.
A new condition should not change the main algorithm.
Nulls

Solutions

Polymorphism
Create hierarchies/compose objects following Open closed principle.
Use State pattern to model transitions.
Use Strategy Pattern/Method Object to choose for branches.

Examples

Discrete Values
State transition
Algorithm choice.

Sample Code

Wrong

class Mp3Converter {
  convertToMp3(source, mimeType) {
    if(mimeType.equals("audio/mpeg")) {
        this.convertMpegToMp3(source)
    } else if(mimeType.equals("audio/wav")) {
        this.convertWavToMp3(source)
    } else if(mimeType.equals("audio/ogg")) {
        this.convertOggToMp3(source)
    } else if(...) {
        // Lots of new clauses
}

Right

class Mp3Converter {
  convertToMp3(source, mimeType) {
    const foundConverter = this.registeredConverters.
        find(converter => converter.handles(mimeType));
        // Do not use metaprogramming to find and iterate converters
        // since this is another problem.    
    if (!foundConverter) {
      throw new Error('No converter found for ' + mimeType);
    }    
    foundConverter.convertToMp3(source);
  }
}

#Detection

Since there are valid cases for If/else usages, we should not pull the plug and forbid these instructions. We can put a ratio of if statements/other statements as a warning instead.