Feature Flags: A Potential Source of Evil and Zombie-Like Resurrections TL;DR: Don't leave lingering. Clean up your feature flag debris. unused code The Problems Dead Code Maintainability Unnecessary complexity Proposed Solutions Clean out dead code Establish a clear lifecycle for your feature flags Background are commonly used to certain features or functionalities on or off dynamically, allowing for controlled rollouts or . Feature flags toggle A/B testing However, if the code regulated by these flags becomes obsolete or is no longer necessary, it can result in dead code. Not only does dead code clutter the codebase, making it more challenging to understand and maintain, but it can also confuse developers, giving the false impression that certain functionalities are still active and supported when they aren't. A notable example of this occurred with the . Old code, left active under a feature flag alongside new code, caused the system to send a massive volume of incorrect orders to the market, leading to losses of approximately $440 million for Knight Capital Group in a matter of minutes, nearly resulting in bankruptcy for the firm. Knight Capital Group Sample Code Incorrect Approach public class WeatherSimulation {
    private boolean isWeatherSimulationEnabled ; 
    // This feature flag controls weather simulation
  
    public WeatherSimulation() {
        Properties config = new Properties();
        FileInputStream fis = new FileInputStream("config.properties")) {
            config.load(fis);
            isWeatherSimulationEnabled = Boolean.parseBoolean(
                config.getProperty("weatherSimulation.enabled", "false"));
            // The feature toggle is read from the file
            isWeatherSimulationEnabled = false;
        }
    }
   
    public void simulateWeather() {
        if (isWeatherSimulationEnabled) {
            // Code to simulate weather conditions
            // ...
            System.out.println("Simulating weather...");
        }
    }
} Correct Approach public class WeatherSimulation {
  
    public WeatherSimulation() {
        Properties config = new Properties();
        FileInputStream fis = new FileInputStream("config.properties")) {
            config.load(fis);
            String weatherSimulationEnabledValue = 
              config.getProperty("weatherSimulation.enabled");
            if (weatherSimulationEnabledValue != null) {
                throw new IllegalStateException(
                  "weatherSimulation.enabled property " + 
                  "should not be present in the configuration file.");
                // Follow the fail-fast principle. 
                // The feature is deprecated 
                // and users have been notified during the grace period
                // After this period, execution should be stopped              
            }
        }
    }
   
    public void simulateWeather() {
       // Remove the simulated code and simplify it
    }
} Detection Semi-Automatic [x] Employ mutation testing and remove potential dead code to see if your coverage net identifies a defect. Tags Bloaters Level Intermediate [x] AI Assistants AI assistants usually don't add dead code or feature flags unless explicitly instructed to do so. Conclusion Regularly review and clean up feature flags and associated code to eliminate unnecessary or obsolete parts. This ensures that the code remains lean, comprehensible, and free from potential issues caused by dead code. Feature flags should have a short lifespan and their lifecycle must be supervised. Relations Code Smell 09 - Dead Code Code Smell 29 - Settings / Configs Additional Information https://dougseven.com/2014/04/17/knightmare-a-devops-cautionary-tale/?embedable=true Disclaimer - Code Smells reflect my . opinion Credits - Photo by on the blowup Unsplash "The software isn’t finished until the last user is dead." Sidney Markowitz https://hackernoon.com/400-thought-provoking-software-engineering-quotes?embedable=true This article is part of the CodeSmell Series. https://hackernoon.com/how-to-find-the-stinky-parts-of-your-code-part-i-xqz3evd?embedable=true

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