updating final values

main.dart

void main() {
  final order1 = Order(
    address: Address(
      street: "Daguan",
      city: "Taipei",
      postcode: "231",
      country: "Taiwan"
    ),
    person: Person(
      firstName: "Chloe",
      lastName: "Hsu"
    )
  );
  
  final order2 = order1.update(
    address: order1.address.update(
      street: "Shida",
      postcode: "106"
    )
  );
}

class Order {
  final Address address;
  final Person person;
  
  Order({this.address, this.person});
  
  update({Address address, Person person}) =>
    Order(
      address: address ?? this.address,
      person: person ?? this.person
    );
}

class Address {
  final String street;
  final String city;
  final String postcode;
  final String country;
  
  Address({this.street, this.city, this.postcode, this.country});
  
  update({String street, String city, String postcode, String country}) =>
    Address(
      street: street ?? this.street,
      city: city ?? this.city,
      postcode: postcode ?? this.postcode,
      country: country ?? this.country
    );
}

class Person {
  final String firstName;
  final String lastName;
  
  Person({this.firstName, this.lastName});
}