Initialize enum from associated value

user_14087244 0
Viewed 3646

I would like to initialize enum by its associated value.

My enum:

enum class DirectionSwiped(raw: Int){
    LEFT(4),
    RIGHT(8);
}

I would like to initialize it as such:

val direction = DirectionSwiped(raw: 4)

But I get this error:

Enum type cannot be instantiated

Why is this happening? In Swift, this functionality works like this:

enum Direction: Int {
    case right = 2
}

let direction = Direction(rawValue: 2)

How can I make it work in Kotlin?

kotlin enums
2 Answers

Yes you can

enum class DirectionSwiped(val raw: Int){
    LEFT(4),
    RIGHT(8);
}

val left = DirectionSwiped.LEFT
val right = DirectionSwiped.RIGHT

val leftRaw = DirectionSwiped.LEFT.raw
val rightRaw = DirectionSwiped.LEFT.raw

val fromRaw = DirectionSwiped.values().firstOrNull { it.raw == 5 }

This would be the correct way to access the instances of the enum class

What you are trying to do is create a new instance outside the definition site, which is not possible for enum or sealed classes, that's why the error says the constructor is private

user_18537850

As the error says, you cannot instantiate enums in Kotlin. A possible workaround would be to use a map and 2 helper methods to get enum values from raw values and vice versa:

enum class DirectionSwiped {
    LEFT,
    RIGHT;

    fun toRaw() = enumToRaw[this]
    companion object {
        val rawToEnum = mapOf(
                4 to LEFT,
                8 to RIGHT
        )
        val enumToRaw = rawToEnum.entries.associate{(k,v)-> v to k}
        fun ofRaw(raw: Int): DirectionSwiped? = rawToEnum[raw]
    }
}

Usage:

val direction = DirectionSwiped.ofRaw(4) // LEFT
val raw = DirectionSwiped.LEFT.toRaw() // 4
user_40307650
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