resettableDelegate.kt

interface IResettable {
    fun reset()
}
 
open class ResettableAspect: IResettable {
        val delegateManager by lazy {
            ResettableDelegateManager()
        }
        override fun reset() {
            delegateManager.reset()
        }
    }

class ResettableDelegateManager : IResettable {
    val delegates = LinkedList<IResettable>()

    override fun reset() {
        delegates.forEach {
            it.reset()
        }
    }

    fun <PROPTYPE> register(instance: ResettableDelegate<PROPTYPE>) {
        delegates.add(instance)
    }
}

class ResettableDelegate<PROPTYPE>(sourceManager: ResettableDelegateManager, val init: () -> PROPTYPE) : ReadWriteProperty<Any?, PROPTYPE>, IResettable {
    init {
        sourceManager.register(this)
    }

    var currentValue = init()

    override operator fun getValue(thisRef: Any?, property: KProperty<*>): PROPTYPE {
        return currentValue
    }

    override fun setValue(thisRef: Any?, property: KProperty<*>, value: PROPTYPE) {
        currentValue = value
    }

    override fun reset() {
        currentValue = init()
    }
}

// usage
object Measurement: ResettableAspect() {
    var loadTimeStart by ResettableDelegate(delegateManager) { 0L }
    var loadTimeEnd by ResettableDelegate(delegateManager) { 0L }
}

fun main() {
  Measurement.loadTimeStart = now() // presudo
  ...
  Measurement.loadTimeEnd = now() // presudo
  val diff = Measurement.loadTimeEnd - Measurement.loadTimeStart
  println("it takes $diff ms!)

  Measurement.reset()
}