The argument type 'List<dynamic>' can't be assigned to the parameter type 'FutureOr<List<T>>?'

Question

I am trying to write a generic cache utility using sembast. Follwoing is the code:

import 'package:sembast/sembast.dart';
import 'package:tachyon/core/domain/trait/map_serializer.dart';
class CachingController<T> {
  final Database _cache;
  final StoreRef<String, Map<String, dynamic>> _store =
      stringMapStoreFactory.store('objects');

  CachingController(this._cache);

  Future<void> insertObjects(
      MapSerializer mapSerializer, List<T> objectList) async {
    final objectMap =
        objectList.map((object) => mapSerializer.toMap(object)).toList();
    await _store.addAll(_cache, objectMap);
  }

  Future<List<T>> getObjects(MapSerializer mapSerializer) async {
    final finder = Finder(sortOrders: [SortOrder('phone_number')]);
    final records = await _store.find(_cache, finder: finder);
    final objectList =
        records.map((record) => mapSerializer.fromMap(record.value)).toList();
    return Future.value(objectList);
  }
}

The abstract MapSerializer class is:

abstract class MapSerializer<T> {
  Map<String, dynamic> toMap(T item);
  T fromMap(Map<String, dynamic> json);
}

But in the getObjects method of CachingController<T> I am getting this compiler error at the return statement.

The argument type 'List<dynamic>' can't be assigned to the parameter type 'FutureOr<List<T>>?'.

which goes away if I change the return statement to return Future.value(objectList as FutureOr<List<T>>?); by adding casting but it doesn't seem to the correct way to do it.

I would love to have suggestion on what should be done here.

Answer 1

  Future<List<T>> getObjects(MapSerializer<T> mapSerializer) async {
    final finder = Finder(sortOrders: [SortOrder('phone_number')]);
    final records = await _store.find(_cache, finder: finder);
    final objectList =
        records.map((record) => mapSerializer.fromMap(record.value)).toList();
    return Future.value(objectList);
  }

can you add T in the function argument MapSerializer<T> mapSerializer like this?