class Person {
  int? id;
  String name;
  String birthday;
  int? age;

  Person({required this.name, this.id, required this.birthday, this.age});

  // Redirecting Constructor
  Person.clone(Person person) :
      this(
          id: person.id,
          name: person.name,
          birthday: person.birthday,
          age: person.age
      );

  Map<String, dynamic> toMap() {
    return {
      "id": id,
      "name": name,
      "birthday": birthday,
      //"age": age,
    };
  }
}

void main() {
  Person p1 = Person(id: 1, name: "Aiden", birthday: "2020/01/01", age: 2);
  Person p2 = p1;
  
  print(p1.age);
  print(p2.age);
  
  p1.age = 3;
  
  print(p1.age);
  print(p2.age);
  
  print("-------------------------");
  
  Person p3 = Person.clone(p1);
  
  print(p1.age);
  print(p3.age);
  
  p1.age = 1;
  
  print(p1.age);
  print(p3.age);
}

2
2
3
3
-------------------------
3
3
1
3