fbe_dart_iterables_change_expand

hint.txt

Try using `expand` to transform a list of orders into a list of those order's items.

main.dart

/// These classes do not need to be changed.
class Customer {
  final List<Order> pastOrders;

  Customer(this.pastOrders);
}

class Order {
  final List<Item> itemsPurchased;

  Order(this.itemsPurchased);
}

class Item {
  final String name;
  final int cost;

  Item(this.name, this.cost);
}

/// Start your edits here
List<Item> extractItemsFromOrdersForCustomer(Customer customer) {
  // implement
}

solution.dart

List<Item> extractItemsFromOrdersForCustomer(Customer customer) {
  final items = customer.pastOrders.expand((Order o) => o.itemsPurchased).toList();
  return items;
}

test.dart

void main() {
  final allLineItemsFromCustomer = extractItemsFromOrdersForCustomer(customer);
  if (allLineItemsFromCustomer is! List<Item>) {
    _result(false, ['the function did not return a List<Item> type']);
  }
  if (allLineItemsFromCustomer.length != 4) {
    _result(false, [
      'the function extractItemsFromOrdersForCustomer should have returned a list of length 4',
      'Got a list of length ${allLineItemsFromCustomer.length}.'
    ]);
  }

  _result(true, ['All tests passed!', 'Good job, fam']);
}