Tell me about the development of the feature toggle mechanism.

Feature toggle — a mechanism for enabling and disabling application functionality without deployment. It allows flexible management of features, conducting A/B tests, and gradual releases.

Main steps of the mechanism development:

1. Defining toggle points — in the code where the feature's state needs to be checked.
2. Storing feature state — can use configuration files, databases, external services.
3. API for checking — a method that returns whether the feature is enabled for the current user/session.
4. Managing strategies — for example, enabling for all, for some users, by time.
5. Integration with CI/CD — to quickly change the state without release.

Example of a simple toggle:

public class FeatureToggle {
    private static final Map<String, Boolean> features = Map.of(
        "newUI", true,
        "betaFeature", false
    );

    public static boolean isEnabled(String featureName) {
        return features.getOrDefault(featureName, false);
    }
}

// Usage
if (FeatureToggle.isEnabled("newUI")) {
    // new interface
} else {
    // old interface
}

For advanced solutions, third-party libraries and services are used, such as LaunchDarkly, Unleash.