Optional<T> in Kotlin using a Sealed Class

Nice quick way to add Guava or Android API24’s Optional<T> using Kotlin’s sealed classes (until they build this into the languate as a Maybe class):

sealed class Option<out A> {
    object None : Option<Nothing>()
    data class Value<out A>(val value: A) : Option<A>()

    companion object {
        fun <A>from(value: A?): Option<out A> {
            return value?.let { Value(value) } ?: None
        }
    }
}

Usage is pretty simple…just do Option.from<YourClass> on any value that may be nullable. Then you can use this to pass through a reactive stream since you can’t pass nulls through; on the other wise, unwrap it with:

when (it) {
     is Value ->
           val value = it.value
     is None ->
           // handle error
}