Refined types in Kotlin

RefinedTypes.kt

class Refined<A : Any>(
    default: A,
    private val errorMsgGen: (A) -> String = {
        "Value: $it does not meet its constraints!"
    },
    private val validator: (A) -> Boolean = { true }
) : ReadWriteProperty<Refined<A>?, A> {
    private var backingField: A = default

    override operator fun getValue(thisRef: Refined<A>?, property: KProperty<*>): A {
        return backingField
    }

    override operator fun setValue(thisRef: Refined<A>?, property: KProperty<*>, value: A) {
        if (validator(value)) {
            backingField = value
        } else {
            throw IllegalStateException(errorMsgGen(value))
        }
    }
}

// this will allow to enhance the error message with the typename
// a bit of experimentation with the `thisRef` showed that it
// always returns null 
inline fun <reified A : Any> Refined(
    default: A,
    noinline validator: (A) -> Boolean
): Refined<A> {
    return Refined(
        default,
        {
            "Value: $it does not meet type: ${A::class.java.simpleName} constraints!"
        },
        validator
    )
}

fun PositiveInt() =
    Refined(0) { it > 0 }

fun NegativeInt() =
    Refined(0) { it < 0 }

fun <A> NonEmptyList(vararg elements: A) =
    Refined(elements.toList()) { it.isNotEmpty() }


fun main() {
// usage example
  var positiveInteger: Int by NegativeInt()

  positiveInteger = -1

  var nel: List<String> by NonEmptyList("this", "is", "a", "test")  
}