Effective Enums in Kotlin with reverse lookup?

Question

I\'m trying to find the best way to do a \'reverse lookup\' on an enum in Kotlin. One of my takeaways from Effective Java was that you introduce a static map inside the enum

Answer 1

A slightly extended approach of the accepted solution with null check and invoke function

fun main(args: Array) {
    val a = Type.A // find by name
    val anotherA = Type.valueOf("A") // find by name with Enums default valueOf
    val aLikeAClass = Type(3) // find by value using invoke - looks like object creation

    val againA = Type.of(3) // find by value
    val notPossible = Type.of(6) // can result in null
    val notPossibleButThrowsError = Type.ofNullSave(6) // can result in IllegalArgumentException

    // prints: A, A, 0, 3
    println("$a, ${a.name}, ${a.ordinal}, ${a.value}")
    // prints: A, A, A null, java.lang.IllegalArgumentException: No enum constant Type with value 6
    println("$anotherA, $againA, $aLikeAClass $notPossible, $notPossibleButThrowsError")
}

enum class Type(val value: Int) {
    A(3),
    B(4),
    C(5);

    companion object {
        private val map = values().associateBy(Type::value)
        operator fun invoke(type: Int) = ofNullSave(type)
        fun of(type: Int) = map[type]
        fun ofNullSave(type: Int) = map[type] ?: IllegalArgumentException("No enum constant Type with value $type")
    }
}