kotlin contracts

import kotlin.contracts.ExperimentalContracts
import kotlin.contracts.contract

open class Base

class ChildOne: Base() {
    fun childOneFunc() {
        println("salut")
    }
}

class ChildTwo: Base()

@OptIn(ExperimentalContracts::class)
fun funcThatExitsIfNotChildTwo(inst: Base) {
    contract {
        returns() implies (inst is ChildOne)
    }

    if (inst !is ChildOne) {
        error("nu e")
    }
}

fun main() {
    val inst: Base = ChildOne()
    funcThatExitsIfNotChildTwo(inst)

    inst.childOneFunc()
}