Dart: generics abstract static methods

Question

Dears

I want to have abstract generic class with the following pattern My phone model is as follows:

  class Phone extends ModelInterface {
  ...

  @override
  static dynamic getErrorInstance(Map<String, dynamic> map) {
    return Phone.fromErrors(map);
  }

  @override
  static dynamic getResponseInstance(Map<String, dynamic> map) {
    return Phone.fromMap(map);
  }
}

As you can see the Phone model extends ModelInterface and there are two overriden methods getErrorInstance and getResponseInstance

These two methods are defined as static in the ModelInterface abstract class

abstract class ModelInterface {
  static dynamic getErrorInstance(Map<String, dynamic> map) {}
  static dynamic getResponseInstance(Map<String, dynamic> map) {}
}

What I wanted to do is to create a generic method that builds the object based on response type shown below

abstract class Base {
  ...

  T getModel<T extends ModelInterface>(Map<String, dynamic> map) {
    if (hasErrors(map)) {
      return T.getErrorInstance(map);
    }

    return T.getResponseInstance(map);
  }
}

And the client for this method getModel shown below

class UserAuth extends Base {
  Future<Phone> registerPhone(Phone phone) async {
    String url = Routes.phoneUrl;
    String body = json.encode(phone.toMap());
    final response = await http.post(url, body: body, headers: Routes.headers);
    final responseBody = json.decode(response.body);
    // here I want the generic type to be phone
    return getModel<Phone>(responseBody);
  }
}

However I am getting this error

Thanks

xiarnousx xiarnousx · Accepted Answer · 2019-07-25T09:25:18

Actually I fixed it by passing in another generic Parameter such as below

  T getModel<T extends ModelInterface>(Map<String, dynamic> map, T) {
    if (hasErrors(map)) {
      return T.getErrorInstance(map);
    }

    return T.getResponseInstance(map);
  }

And for the client code I added the below

class UserAuth extends Base {
  Future<Phone> registerPhone(Phone phone) async {
    String url = Routes.phoneUrl;
    String body = json.encode(phone.toMap());
    final response = await http.post(url, body: body, headers: Routes.headers);
    final responseBody = json.decode(response.body);

    return getModel<Phone>(responseBody, Phone.empty());
  }
}

Dart: generics abstract static methods

1 Answers