Chainable lateinit

ln.kt

class Lateinit<T> {

    private var value: T? = null
    private var dependants = mutableListOf<Dependant<T, *>>()

    operator fun getValue(thisRef: Any?, kprop: KProperty<*>): T =
        value ?: throw Exception()

    operator fun setValue(thisRef: Any?, kprop: KProperty<*>, v: T) {
        value = v
        dependants.forEach { d ->
            d.initialize(v)
        }
    }

    fun depend(d: Dependant<T, *>) {
        dependants.add(d)
    }

}

class Dependant<A, T>(private val init: (A) -> T) {
    private var value: T? = null
    fun initialize(dep: A) {
        value = init(dep)
    }
}

fun <T> late(): Lateinit<T> = Lateinit()

fun <A, T> lateDependOn(a: Lateinit<A>, init: (A) -> T): Dependant<A, T> {
    val d = Dependant(init)
    a.depend(d)
    return d
}