I find myself wishing for a `union` type - I know ...

# getting-started

[v79]

I find myself wishing for a union type - I know it's not coming. Can anyone think of a less verbose way of implementing these combination of sealed classes?

val modifiers: MutableMap<String,Attribute> = mutableMapOf()
sealed class Attribute {
	data class fValue(val value: Float) : Attribute() {
		override fun toString(): String {
			return value.toString()
		}
	}
	data class iValue(val value: Int): Attribute()	{
		override fun toString(): String {
			return value.toString()
		}
	}
	data class sValue(val value: String): Attribute() {
		override fun toString(): String {
			return value.toString()
		}
	}
	data class bValue(val value: Boolean): Attribute() {
		override fun toString(): String {
			return value.toString()
		}
	}
	data class lValue(val value: Long) : Attribute() {
		override fun toString(): String {
			return value.toString()
		}
	}
}

[Kroppeb]

Untitled

Untitled

[Kroppeb]

it does seem that this will cause boxing for getValue() which might be a bug?

[v79]

I've been avoiding Any because these will all be serialized to json.

[Kroppeb]

Using kotlin serialization or something else?

[v79]

Yes, kotlinx serialization.

[Mark Murphy]

data class defines its own toString() which clobbers the one in Attribute.

Here is my take:

sealed class Attribute<T>(open val value: T) {
	override fun toString() = value.toString()

	class fValue(override val value: Float) : Attribute<Float>(value)

	class iValue(override val value: Int): Attribute<Int>(value)

	class sValue(override val value: String): Attribute<String>(value)

	class bValue(override val value: Boolean): Attribute<Boolean>(value)

	class lValue(override val value: Long) : Attribute<Long>(value)
}

[Kroppeb]

oh true, but you can make toString final in Attribute

[Kroppeb]

and i think we are still causing unnesesairy boxing

[Mark Murphy]

another option is to skip the sealed class and use a private constructor to control what types are valid:

class Attribute<T> private constructor(val value: T) {
	override fun toString() = value.toString()
  
  companion object {
    fun of(value: Float) = Attribute(value)
    fun of(value: Int) = Attribute(value)
    fun of(value: String) = Attribute(value)
    fun of(value: Boolean) = Attribute(value)
    fun of(value: Long) = Attribute(value)
  }
}