Named Constructors trong Dart

class ClassName {
  ClassName.constructorName() {
    // initialization
  }
}

class Point {
  double x, y;
  
  // Default constructor
  Point(this.x, this.y);
  
  // Named constructors
  Point.origin() : x = 0, y = 0;
  
  Point.onXAxis(double x) : this.x = x, y = 0;
  
  Point.onYAxis(double y) : x = 0, this.y = y;
}
 
void main() {
  var p1 = Point(3, 4);
  var p2 = Point.origin();
  var p3 = Point.onXAxis(5);
  var p4 = Point.onYAxis(10);
}

class User {
  String name;
  int age;
  String email;
  
  User(this.name, this.age, this.email);
  
  User.fromJson(Map<String, dynamic> json)
      : name = json['name'],
        age = json['age'],
        email = json['email'];
}
 
void main() {
  var json = {'name': 'Alice', 'age': 25, 'email': 'alice@email.com'};
  var user = User.fromJson(json);
}

class User {
  String name;
  int age;
  
  User(this.name, this.age);
  
  User.fromJson(Map<String, dynamic> json)
      : name = json['name'],
        age = json['age'];
  
  Map<String, dynamic> toJson() {
    return {'name': name, 'age': age};
  }
}

class Person {
  String name;
  int age;
  
  Person(this.name, this.age);
  
  // Copy constructor
  Person.copy(Person other)
      : name = other.name,
        age = other.age;
  
  // copyWith pattern
  Person copyWith({String? name, int? age}) {
    return Person(
      name ?? this.name,
      age ?? this.age,
    );
  }
}
 
void main() {
  var original = Person('Alice', 25);
  var copy = Person.copy(original);
  var modified = original.copyWith(age: 26);
}

class Event {
  String title;
  DateTime date;
  
  Event(this.title, this.date);
  
  Event.now(this.title) : date = DateTime.now();
  
  Event.tomorrow(this.title) 
      : date = DateTime.now().add(Duration(days: 1));
  
  Event.scheduled(this.title, int year, int month, int day)
      : date = DateTime(year, month, day);
}

class Config {
  String host;
  int port;
  bool secure;
  
  Config({
    required this.host,
    this.port = 80,
    this.secure = false,
  });
  
  Config.development()
      : host = 'localhost',
        port = 3000,
        secure = false;
  
  Config.production()
      : host = 'api.example.com',
        port = 443,
        secure = true;
}