Typed event listeners example In the beginning of this article we also mentioned the addEventListener function, so for the sake of completeness, let's also apply our new knowledge to it. Here, we use type parameter to specify listener function type:

Main.hx

import haxe.Constraints.Function;

abstract Event<T:Function>(String) {
  public inline function new(name) {
    this = name;
  }
}

extern class EventEmitter {
  function new();
  function addEventListener<T:Function>(event:Event<T>, listener:T):Void;
}

class Main {
  static inline var EVENT_START = new Event<Array<String>->Void>("start");
  static inline var EVENT_EXIT = new Event<Int->Void>("exit");

  static function main() {
    var emitter = new EventEmitter();

    // arr is inferred as Array<String>
    emitter.addEventListener(EVENT_START, function(arr) trace(arr));

    // compile error: String -> Void should be Int -> Void
    // emitter.addEventListener(EVENT_EXIT, function(s:String) {});
  }
}