Named Constructors trong Dart

class Point {
  double x, y;
  
  Point(this.x, this.y);
  
  // Named constructors
  Point.origin() : x = 0, y = 0;
  
  Point.fromJson(Map<String, double> json)
      : x = json['x'] ?? 0,
        y = json['y'] ?? 0;
}
 
var p1 = Point.origin();
var p2 = Point.fromJson({'x': 10, 'y': 20});

class User {
  final String id;
  final String name;
  final String email;
  
  User({
    required this.id,
    required this.name,
    required this.email,
  });
  
  User.fromJson(Map<String, dynamic> json)
      : id = json['id'],
        name = json['name'],
        email = json['email'];
  
  Map<String, dynamic> toJson() => {
    'id': id,
    'name': name,
    'email': email,
  };
}