Kotlin - Data class type String or some Object - kotlin

Question

Say I have this data class in Kotlin:
#Document(collection = Approval.COLLECTION)
data class Approval(
#Id
val id: String,
val detailId: <UNSURE HERE>
) {
companion object {
const val COLLECTION: String = "approval"
}
}
That detailID can either be a String or an object like so:
data class AIDConfiguration(
val sId: String,
val cId: String
)
However how do go about setting that type - as I can't use something like
val detailId: AIDConfiguration | String
I thought maybe make an interface, but not sure any syntax of getting that to be just a String
interface ParentConfiguration
data class AIDConfiguration(
val sId: String,
val cId: String
): ParentConfiguration
And then
val detailId: ParentConfiguration
Any help appreciated.
Thanks.

Answer 1

One way could be:
val detailId: Any
This is loose cause it will allow any type to be assigned to detailId.
So before usage you would have to check for the type.
fun useConfig(detailId: Any) {
if (detailId is AIDConfiguration) {
//Use detailId.sId and detailId.cId. Compiler smart casts to AIDConfiguration
} else if (detailId is String)
//Use detailId. Compiler will smart cast to String
} else {
//throw some exception here.
}
}
You might want to use some validations when setting the configuration as well. Check whether the type is AIDConfiguration or String.
A little more tighter would be to have a parent configuration class. Such as ParentConfiguration and have AIDConfiguration and StringConfiguration as subclasses.
So then it becomes:
interface ParentConfiguration
data class AIDConfiguration(
val sId: String,
val cId: String
): ParentConfiguration
data class StringConfiguration(
val conf: String
): ParentConfiguration
data class Approval(
val id: String,
val detailId: ParentConfiguration
)
val stringConfigApproval = Approval(id = "Test1", detailId = StringConfiguration("String Conf"))
val aidConfApproval = Approval(id = "Test2", detailId = AIDConfiguration(sId = "SID", cId = "CID"))
Would recommend checking out the kotlin docs.
https://kotlinlang.org/docs/tutorials/kotlin-for-py/inheritance.html
https://kotlinlang.org/docs/reference/typecasts.html

Answer 2

Kotlin being a statically typed language, you can't just specify multiple types. An interface is a good option to do so, but since String is not implemented by you, you cannot change its signature.
One of the work around should be to use Either like this:
sealed class Either<out L, out R> {
data class Left<out L>(val a: L) : Either<L, Nothing>()
data class Right<out R>(val b: R) : Either<Nothing, R>()
/**
* Returns true if this is a Right, false otherwise.
* #see Right
*/
val isRight get() = this is Right<R>
/**
* Returns true if this is a Left, false otherwise.
* #see Left
*/
val isLeft get() = this is Left<L>
/**
* Applies fnL if this is a Left or fnR if this is a Right.
* #see Left
* #see Right
*/
fun fold(fnL: (L) -> Any, fnR: (R) -> Any): Any =
when (this) {
is Left -> fnL(a)
is Right -> fnR(b)
}
}
And then specify your variable like this:
val detailId: Either<AIDConfiguration, String>
And when you want to do some specific operation, just call the fold method like:
detailId.fold({ /* use $it as AIDConfiguration */ }, { /* use $it as String */ })
EDIT: You could also make aliases for your purpose in your projects for better readability check https://kotlinlang.org/docs/reference/type-aliases.html