Retrieve the user ids of those whose ages are an even number

main.dart

import 'package:collection/collection.dart';

// Given an array of User HashMaps with keys of Id and Age,
// write in Dart the code to return an array of User Ids for
// users whose Age is an even number. Make the code as efficient and terse as possible.
List<int> evenAgedUserIds(List<Map<String, dynamic>> usersEntries) {
  return usersEntries
      // ignore: avoid_dynamic_calls
      .where((userEntry) => userEntry['age'] % 2 == 0)
      .map((userEntry) => userEntry['id'] as int)
      .toList();
}

void main() {
  // Comparing two lists in dart [1, 2] == [1, 2] with default equality doesn't
  // actually work because it compares references. So instead, this does value
  // comparison considering them a closed set.
  Function listEquals = const ListEquality().equals;
  final exampleUsers1 = <Map<String, dynamic>>[
    {"id": 1, "age": 21},
    {"id": 2, "age": 42},
    {"id": 3, "age": 20},
  ];
  final exampleUsers2 = <Map<String, dynamic>>[
    {"id": -1, "age": 21},
    {"id": 0, "age": 2},
    {"id": double.infinity, "age": double.infinity},
    {"id": 17, "age": 0},

    // I didn't purposefully handle this case as requirements were for terseness.
    // Although, in production I would definitely prefer complete type safety to
    // avoid runtime errors:
    // {"id": null , "age": null},
  ];

  // I would actually use https://pub.dev/packages/test here to test but I don't think
  // dartpad supports that package.
  assert(listEquals(evenAgedUserIds(exampleUsers1), [2, 3]));
  assert(listEquals(evenAgedUserIds(exampleUsers2), [0, 17]));
}