how to convert to NotNull by using enum in Kotlin - enums

Question

How can I convert the following code to accepted NotNull inside enum class by using Kotlin?
Note: i'm using this enum between two activity and one activity has 2 adapters.
Here is enum class
enum class Adapterx {
ADAPTER_1,
ADAPTER_2;
companion object {
fun fromOrdinal(ordinal: Int): Adapterx? {
return Adapterx.values().firstOrNull { it.ordinal == ordinal }
}
}
}

Answer 1

Since you cannot restrict the ordinal: Int parameter as you've define it, you have two choices if you receive an ordinal which is not part of the enum, or is out of bounds:
Return a default value
Throw an exception
IMHO both cases are plausible if you document properly the method.
Here's a case where you return just a default value if you ask for an ordinal that does not exist:
class KotlinEnumTest {
enum class Adapterx {
ADAPTER_1,
ADAPTER_2;
companion object {
val defaultValue = ADAPTER_1
fun fromOrdinal(ordinal: Int): Adapterx =
Adapterx.values().getOrElse(ordinal, { _ -> defaultValue })
}
}
#Test fun testEnumOrdinals() {
val resultAdapter1 = Adapterx.fromOrdinal(0)
Assert.assertEquals(Adapterx.ADAPTER_1, resultAdapter1)
val resultAdapter2 = Adapterx.fromOrdinal(1)
Assert.assertEquals(Adapterx.ADAPTER_2, resultAdapter2)
// The following returns the default value ADAPTER_1
val resultOrdinalIndexOutOfBounds = Adapterx.fromOrdinal(2)
Assert.assertEquals(Adapterx.ADAPTER_1, resultOrdinalIndexOutOfBounds)
}
}