Dart Callback

callback-demo.dart

class Event {
  
}

class SomeComponent {
  
  // Q: How to express the type of _callback?
  var _callback = (Event e) { /* dummy implementation */};

  // Called to register a callback
  void onEvent( void callback(Event e) ) {
    print("Registering callback...");
    _callback = callback;
  }
  
  // Called to fire the event
  void fireEvent() {
    print("Fire!");
    Event e = new Event();
    _callback(e);
  }
  
}

void main() {
  
  var c = new SomeComponent();
  c.onEvent((Event e){
    print("The event $e has been fired!");
  });
  
  // On some other part of the program...
  c.fireEvent();
  
}