gistfile1.txt

class SerializableObservable<T : Serializable>(private val onChange: (oldValue: T?, newValue: T?) -> Unit) : ReadWriteProperty<Any?, T?>, Serializable {

    var value: T? = null

    override fun getValue(thisRef: Any?, property: KProperty<*>): T? {
        return value
    }

    override fun setValue(thisRef: Any?, property: KProperty<*>, value: T?) {
        val old = this.value
        this.value = value
        onChange.invoke(old, this.value)
    }
}