Strictly typed event handlers

A.md

Try Haxe

Test.hx

class Test {
  static function main() {
    addEventListener(MouseEventType, function(e:MouseEvent) {});
    addEventListener(KeyboardEventType, function(e:KeyboardEvent) {});
    // addEventListener(MouseEventType, function(e:KeyboardEvent) {}); // error: MouseEvent should be KeyboardEvent
  }
  
  static function addEventListener<T:EventBase>(
    eventType:EventType<T>,
    handler:T->Void
  ):Void {trace(eventType);}
}

class EventBase {}
class MouseEvent extends EventBase {}
class KeyboardEvent extends EventBase {}

enum abstract EventType<T:EventBase>(String) to String {
  var MouseEventType:EventType<MouseEvent> = "mouseevent";
  var KeyboardEventType:EventType<KeyboardEvent> = "keyboardevent";
}