class SingleEvent<T> {
  SingleEvent({required Function(T? param) invoke}) : _invoke = invoke;

  final Function(T? param) _invoke;

  bool _isClosed = false;
  bool get isClosed => _isClosed;

  void invokeWith(T? param) {
    if (!_isClosed) {
      _invoke(param);
    }
  }

  void invoke() {
    if (!_isClosed) {
      _invoke(null);
    }
  }

  void close() {
    _isClosed = true;
  }
}