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

Based on your example, i might suggest removing the associated value and just use the ordinal which is similar to an index.

ordinal - Returns the ordinal of this enumeration constant (its position in its enum declaration, where the initial constant is assigned an ordinal of zero).

enum class NavInfoType {
    GreenBuoy,
    RedBuoy,
    OtherBeacon,
    Bridge,
    Unknown;

    companion object {
        private val map = values().associateBy(NavInfoType::ordinal)
        operator fun get(value: Int) = map[value] ?: Unknown
    }
}

In my case i wanted to return Unknown if the map returned null. You could also throw an illegal argument exception by replacing the get with the following:

operator fun get(value: Int) = map[value] ?: throw IllegalArgumentException()