Kotlin Code Smell 18 - Arrays Abusers

Kotlin Code Smell 18 - Arrays Abusers

Beyond Arrays: Designing with First-Class Objects

TL;DR: Use arrays for rapid prototyping, use object for serious business.

Problems

  • Coupling

  • Information Hiding

  • Code Duplication

  • Fail Fast

  • Integrity

Solutions

  1. Reify objects

  2. Create cohesive small objects

  3. Avoid anemic objects and identify their cohesive relations.

Sample Code

Wrong

// Array with some raw data, what can go wrong?
val coordinates = arrayOf(1000.0, 2000.0)

Anemic

data class GeographicCoordinate(
    val longitude: Double,
    val latitude: Double 
)

// An error should be thrown since these values don't exist on Earth
val coordinates = GeographicCoordinate(1000.0, 2000.0)

Validated

class GeographicCoordinate(
    val longitude: Double,
    val latitude: Double
) {
    init {
        if (!isValidLatitude(latitude))
            throw InvalidLatitudeException(latitude)
        if (!isValidLongitude(longitude))
            throw InvalidLongitudeException(longitude)
    }

    private fun isValidLatitude(latitude: Double) =
        latitude in -90.0..90.0
    private fun isValidLongitude(longitude: Double) =
        longitude in -180.0..180.0
}

// An error should be thrown since these values don't exist on Earth
val coordinates = GeographicCoordinate(1000.0, 2000.0)

Right

Degrees deserve reification...

data class Latitude(val degree: Double) {
    init {
        if (degree !in -90.0..90.0)
            throw InvalidLatitudeException(degree)
    }
}

data class Longitude(val degree: Double) {
    init {
        if (degree !in -180.0..180.0)
            throw InvalidLongitudeException(degree)
    }
}

data class GeographicCoordinate(
    val longitude: Longitude,
    val latitude: Latitude
)

// An error should be thrown since these values don't exist on Earth
val coordinates = GeographicCoordinate(
    Longitude(1000.0),
    Latitude(2000.0)
)

Many people suffer from primitive obsession and believe this is over-design. Designing software is about making decisions and comparing trade-offs. The performance argument is not valid nowadays since modern virtual machines can efficiently deal with small short-lived objects.

Conclusion

When creating objects, we must not think of them as data. This is a common misconception.

We should stay loyal to our Bijection and discover real-world objects.

Most associative arrays have cohesion and represent real-world entities, and we must treat them as first-class objects.

Credits

Did you find this article valuable?

Support Yonatan Karp-Rudin by becoming a sponsor. Any amount is appreciated!