Issue
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 to handle the reverse lookup. Porting this over to Kotlin with a simple enum leads me to code that looks like this:
enum class Type(val value: Int) {
A(1),
B(2),
C(3);
companion object {
val map: MutableMap<Int, Type> = HashMap()
init {
for (i in Type.values()) {
map[i.value] = i
}
}
fun fromInt(type: Int?): Type? {
return map[type]
}
}
}
My question is, is this the best way to do this, or is there a better way? What if I have several enums that follow a similar pattern? Is there a way in Kotlin to make this code more re-usable across enums?
Solution
First of all, the argument of fromInt()
should be an Int
, not an Int?
. Trying to get a Type
using null will obviously lead to null, and a caller shouldn't even try doing that. The Map
has also no reason to be mutable. The code can be reduced to:
companion object {
private val map = Type.values().associateBy(Type::value)
fun fromInt(type: Int) = map[type]
}
That code is so short that, frankly, I'm not sure it's worth trying to find a reusable solution.
Answered By - JB Nizet
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