An use case for synthetic events in Kotlin

main.kt

/**
 * This is a generic event class. It simply allows subscription and invocation.
 */
class Event<T> {
    private val handlers = arrayListOf<(Event<T>.(T) -> Unit)>()
    operator fun plusAssign(handler: Event<T>.(T) -> Unit) { handlers.add(handler) }
    operator fun invoke(value: T) { for (handler in handlers) handler(value) }
}

/**
 * Each controller would have a companion object which would be the event emitted by
 * each endpoint. The event would be a tuple of the function invoked and its payload.
 */
class SomeController {
    companion object {
        var eventEmitted = Event<Pair<String, String>>()
    }

    fun post(body: Any): String {
        // Ideally this "eventEmitted" invocation could be abstracted away in a parent class?
        eventEmitted(Pair("SomeController::post", "post method invoked"))
        return "Return POST value"
    }

    fun get(): String {
        eventEmitted(Pair("SomeController::get", "get method invoked"))
        return "Return GET value"
    }
}

/**
 * The Notifications is the one which handles which events trigger which logic. Potentially there could
 * be some sugar syntax applied here to not have to do the whole if/then ceremony.
 */
class NotificationsManager {
    fun setupEvents() {
        SomeController.eventEmitted += { if (it.first == "SomeController::get") println("get's event payload >>> ${it.second}") }
        SomeController.eventEmitted += { if (it.first == "SomeController::post") println("post's event payload >>> ${it.second}") }
    }
}

/**
 * Runnable example :)
 */
fun main(args : Array<String>) {
    val controller = SomeController()
    NotificationsManager().setupEvents()
    controller.get()
    controller.get()
    controller.post("")
}