In Kotlin, can a property of a data class have multiple types? For example:
val CurrentValue: Double?|String or val CurrentValue: String|Array?
I cannot find it in the documentation.
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Does this answer your question? Kotlin and discriminated unions (sum types)outis– outis2022-07-22 21:20:51 +00:00Commented Jul 22, 2022 at 21:20
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1 Answer
Union types are not a thing in Kotlin.
You may use a sealed class instead.
sealed class CurrentValue<T>(val value: T) {
class TextualValue(value: String) : CurrentValue<String>(value)
class NumericValue(value: Double) : CurrentValue<Double>(value)
}
Which then you can use exhaustive when expressions (similar to switch in other languages) in order to access the value in a type-safe manner:
fun doSomething(value: CurrentValue<*>) {
when(value) {
is TextualValue -> value.value // is recognised as a String
is NumericValue -> value.value // is recognised as a Double
}
}
If creating a type is way too much for you then you can perform a when statement and treat a parameter based on it's type and perhaps normalize it:
fun parseValue(value: Any?): Double? = when(value){
is Double -> value
is String -> value.toDoubleOrNull()
is Int -> value.toDouble()
else -> null
}
answered Feb 24, 2022 at 21:57
Some random IT boy
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3 Comments
a_local_nobody
this is a pretty nice way of using a sealed class, great answer
Some random IT boy
Still have to see a language that allows so much flexibility while maintaining a strong type system. Kotlin is amazing
NimaAzhd
there is an error. "One type argument expected for class CurrentValue<T>" in where class defined on CurrentValue : class TextualValue(value: String) : CurrentValue(value) I edited your answer a little.