Plain simple events source

Event.kt

import java.util.*
import kotlin.Int
import kotlin.Int as ObserverId

class Event<T>() {
    private val listeners: MutableMap<Int, (T) -> Unit> = HashMap();
    private var nextListenerId: Int = 0

    fun observe(listener: (T) -> Unit): ObserverId {
        synchronized(this.listeners) {
            val id = this.nextListenerId++
            this.listeners[id] = listener
            return id
        }
    }

    fun removeObserver(observerId: ObserverId) {
        synchronized(this.listeners) {
            this.listeners.remove(observerId)
        }
    }

    fun emit(value: T) {
        var listeners = synchronized(this.listeners) { ArrayList(this.listeners.values) }
        for (listener in listeners)
            listener(value)
    }
}

fun test(): Boolean
{
    val r = StringBuilder()
    val kbd = Event<Char>()

    val obs1 = kbd.observe { r.append("1:$it") }
    kbd.emit('1')
    val obs2 = kbd.observe { r.append("2:$it") }

    kbd.emit('2')
    kbd.emit('3')
    kbd.removeObserver(obs1)
    kbd.emit('4')

    return r.toString() == "1:11:22:21:32:32:4" 
}