Kotres provides the Result class for type-safe error handling in Kotlin.
fun parseInt(string: String): Result<Int, NumberFormatException> {
return try {
Success(Integer.parseInt(string))
} catch (e: NumberFormatException) {
Failure(e)
}
}
val number: Result<Int, NumberFormatException> = parseInt(string)
when (number) {
is Success -> print(number.value)
is Failure -> print(number.exception.message)
}
// Monadic methods (`map`, `flatMap`)
val diameter: Result<Double, NumberFormatException> = number.map { 2 * Math.PI * it }
val area: Result<Double, NumberFormatException> = diameter.flatMap { d -> number.map { r -> d * r / 2 } }
// Operators (`mp` as `<$>`, `ap` as `<*>`)
data class Person(val firstName: String, val lastName: String, val age: Int)
val firstName: Result<String, JsonException> = json["firstName"].string
val lastName: Result<String, JsonException> = json["lastName"].string
val age: Result<Int, JsonException> = json["age"].int
val person: Result<Person, JsonException> = curry(::Person) mp firstName ap lastName ap age// Upcasting to a common ancestor
val a: Result<Int, DogException> = Success(2)
val b: Result<Int, CatException> = Failure(CatException())
val sum = a.flatMap { a -> b.map { b -> a + b } } // Result<Int, AnimalException>
// Converting errors
val c: Result<Int, FishException> = Success(3)
val product: Result<Int, FishException> = a
.mapFailure { e -> FishException(e) }
.flatMap { a -> c.map { c -> a * c } }