Kotlin Code Smell 20 - Settings/Configs

Problem

• Duplicated Code

• If Pollution

• Global usage

• Coupling

• Testability and the explosion of testing scenarios

• Complexity

Solution

• Avoid using settings directly

• Create polymorphic objects and inject them externally.

Sample Code

Wrong

class VerySpecificAndSmallObjectThatDealWithPersistence {
    fun retrieveData() =
        if (GlobalSettings.instance["I am A Possible Mistyped String"] != null) {
            retrieveDataThisWay()
        } else {
            retrieveDataTheOtherWay()
        }

    private fun retrieveDataThisWay() {
        // ...
    }

    private fun retrieveDataTheOtherWay() {
        // ...
    }
}

class GlobalSettings {
    private val settings = mutableMapOf<String, String>()

    operator fun set(key: String, value: String) {
        settings[key] = value
    }

    operator fun get(key: String) = settings[key]

    companion object {
        val instance = GlobalSettings()
    }
}

Right

class VerySpecificAndSmallObjectThatDealWithPersistence(private val retrieveStrategy: RetrieveStrategy) {
    fun retrieveData() = retrieveStrategy.retrieve()
}

interface RetrieveStrategy {
    fun retrieve(): String
}

class RetrieveFromDatabase : RetrieveStrategy {
    override fun retrieve(): String {
        return "Data from the database"
    }
}

Examples

• External Connection Settings

• User settings

• Feature Toggle

Exceptions

• Sometimes, we use Feature toggling as a safeguard mechanism. This is acceptable in a legacy system. However, these toggles should be very short-lived in a CI/CD system.

• Hyperparameter settings should be managed by configuration objects. You can read these objects from any persistence media and change your system behavior at runtime in an explicit and controlled way.

Conclusion

Setting runtime behavior is great for software systems.

We should configure our objects so they can behave in different ways, and we should achieve it in an explicit way with explicit behavioral objects.

In this way, our code will be more declarative, clean, and testable. It is not as easy as adding an IF Statement. This kind of lazy developer brings lots of coupling and unexpected issues to our systems.

A system with 300 Boolean configurations has more test combinations (2 ^ 300) than the number of atoms in the universe (10 ^ 80).

Credits

• Code Smell 29 - Settings/Configs by Maximiliano Contieri