Destructuring declarations together with non-trivial custom data classes showcase code.

Destructing custom data classes shall be done with care.

A data class:

data class CarData(
    val wheels: Int,
    val model: String
)

can be destructed:

fun printCar(car: CarData):String{
    val (wheels, model) = car
    return "wheels: $wheels " +
            "- model: $model "
}

(full showcase code in branch destructDeclarationsCustomDataClasses01)

However, adding a new property (name) to the data class:

data class CarData(
    val wheels: Int,
    val name: String, 
    val model: String
)

val trabbi = CarData(4, "something","601")

can cause misleading results if the destructing code remains untouched:

fun printCar(car: CarData):String{
    val (wheels, model) = car
    return "wheels: $wheels " +
            "- model: $model "
}

(full showcase code in branch destructDeclarationsCustomDataClasses02)

Adapting the destruction of car

fun printCar(car: CarData):String{
    val (wheels, model, name) = car
    return "wheels: $wheels " +
            "- model: $model " +
            "- name: $name "
}

improves the code

(full showcase code in branch destructDeclarationsCustomDataClasses03)

Additional ways to improve the fix are

• data class constructor default values

  data class CarData(
      val wheels: Int = 0,
      val name: String = "", // added later
      val model: String = ""
  )

• map by name

  val trabbi = CarData(wheels = 4, name = "trabbi", model = "601")

as in master branch

Run the code

./gradlew run

Run the code

./gradlew test