added PriorityQueue for later use

src/lib/PriorityQueue.hx

@@ -0,0 +1,69 @@
+package lib;
+
+using Lambda;
+
+abstract PriorityQueue<T>(Array<{prio:Float, val:T}>) {
+	public inline function new() {
+		this = [];
+	}
+
+	public function containsElement(element:T):Bool {
+		return this.exists((e) -> e.val == element);
+	}
+
+	public function isEmpty():Bool {
+		return this.length == 0;
+	}
+
+	public function insert(e:T, prio:Float) {
+		this.push({prio: prio, val: e});
+		bubbleUp(this.length - 1);
+	}
+
+	public function extractMin():Null<T> {
+		if (this.length == 0) {
+			return null;
+		}
+
+		swap(0, this.length - 1);
+		var minElement = this.pop();
+
+		bubbleDown(0);
+
+		return minElement.val;
+	}
+
+	private function bubbleUp(index:Int) {
+		var parentIndex:Int = Math.floor((index - 1) / 2);
+
+		if (index > 0 && this[index].prio < this[parentIndex].prio) {
+			swap(index, parentIndex);
+			bubbleUp(parentIndex);
+		}
+	}
+
+	private function bubbleDown(index:Int) {
+		var leftIndex = 2 * index + 1;
+		var rightIndex = 2 * index + 2;
+		var smallest = index;
+
+		if (leftIndex < this.length && this[leftIndex].prio < this[smallest].prio) {
+			smallest = leftIndex;
+		}
+
+		if (rightIndex < this.length && this[rightIndex].prio < this[smallest].prio) {
+			smallest = rightIndex;
+		}
+
+		if (smallest != index) {
+			swap(index, smallest);
+			bubbleDown(smallest);
+		}
+	}
+
+	private function swap(i:Int, j:Int) {
+		var tmp = this[i];
+		this[i] = this[j];
+		this[j] = tmp;
+	}
+}

src/lib/ui/elements/RootElement.hx

@@ -1,7 +1,7 @@
 package lib.ui.elements;
 
 class RootElement implements IUIElement {
-	private var children:Array<IUIElement>;
+	private var children:Array<IUIElement> = [];
 	private final eventManager:UIEventManager = new UIEventManager();
 	private var title:String = "";