Result and OptionalResult sealed classes

Result.kt

package result

import result.Result.Err
import result.Result.Ok

sealed class Result<out T> {
    data class Ok<out T>(val value: T) : Result<T>()
    data class Err(val exception: Exception = RuntimeException(), val msg: String = "") : Result<Nothing>()
}


sealed class OptionalResult<out T> {
    object None : OptionalResult<Nothing>()
    data class Some<out T>(val value: T) : OptionalResult<T>()

}




fun main(args: Array<String>) {

    fun query(id: Int): Result<String> = when (id) {
        1 -> Ok("a result")
        else -> Err(msg = "something went wrong...")
    }


    val result1 = query(1)
    val result2 = query(2)

    val result = result2

    when (result) {
        is Ok -> println("Got ${result.value}")
        is Err -> {
            val (exe, msg) = result
            println("Exception = $exe , msg = $msg")
        }
    }
}

// ##############################################################################

package optionalresult

import optionalresult.OptionalResult.*


sealed class OptionalResult<out T> {
    object None : OptionalResult<Nothing>()
    data class Some<out T>(val value: T) : OptionalResult<T>()
    data class Err(val exception: Exception = RuntimeException(), val msg: String = "") : OptionalResult<Nothing>()

    fun expect(errorMsg: String): T = when (this) {
        is None -> throw IllegalStateException(errorMsg)
        is Err -> throw IllegalStateException(errorMsg)
        is Some -> this.value
    }
}


fun main(args: Array<String>) {

    fun query(id: Int): OptionalResult<String> = when (id) {
        0 -> None
        1 -> Some("a result")
        else -> Err(msg = "something went wrong...")
    }


    val result = query(0)

    when (result) {
        is None -> println("not found")
        is Some -> println("Got ${result.value}")
        is Err -> {
            val (exe, msg) = result
            println("Exception = $exe , msg = $msg")
        }
    }

    lateinit var r : OptionalResult<String>
    lateinit var v: String

//  v =  None.expect("expected: a result") // IllegalStateException: expected a result


//    v =  Err().expect("expected: a result") // IllegalStateException: expected a result

    v = Some("a result").expect("expected: a result") // v has the value "a result"

}