尝试用返回类型替换关键字

Question

将Dart升级到2.3后，我开始出现此错误：

file:///Users/user1/flutter/.pub-cache/hosted/pub.dartlang.org/graphql_flutter-0.9.5/lib/src/widgets/subscription.dart:13:3: Error: Function-typed parameters can't specify 'const', 'final' or 'var' in place of a return type.
Try replacing the keyword with a return type.
  final dynamic error,
  ^^^^^

在此代码中：

typedef SubscriptionBuilder = Widget Function({
  final bool loading,
  final dynamic payload,
  final dynamic error,
});

我该如何解决？我在互联网上找不到与此相关的任何文档。谢谢。