Constructors trong Dart

class Person {
  String name = '';
  int age = 0;
}
 
void main() {
  var person = Person();  // Default constructor
}

class Person {
  String name;
  int age;
  
  // Cách viết đầy đủ
  Person(String name, int age) {
    this.name = name;
    this.age = age;
  }
}

class Person {
  String name;
  int age;
  
  // Cách viết ngắn gọn
  Person(this.name, this.age);
}
 
void main() {
  var person = Person('Alice', 25);
}

class Person {
  String name;
  int age;
  String? city;
  
  Person({
    required this.name,
    required this.age,
    this.city,
  });
}
 
void main() {
  var person = Person(name: 'Bob', age: 30, city: 'Hanoi');
}

class Point {
  double x, y;
  
  Point(this.x, this.y);
  
  Point.origin() : x = 0, y = 0;
  
  Point.fromList(List<double> coords) 
      : x = coords[0], 
        y = coords[1];
}
 
void main() {
  var p1 = Point(3, 4);
  var p2 = Point.origin();
  var p3 = Point.fromList([1, 2]);
}

class Rectangle {
  final double width;
  final double height;
  final double area;
  
  Rectangle(this.width, this.height)
      : area = width * height;
}

class Point {
  double x, y;
  
  Point(this.x, this.y);
  
  // Redirect đến constructor khác
  Point.alongXAxis(double x) : this(x, 0);
  Point.alongYAxis(double y) : this(0, y);
}

class Logger {
  static final Logger _instance = Logger._internal();
  
  factory Logger() {
    return _instance;  // Singleton pattern
  }
  
  Logger._internal();
  
  void log(String message) => print(message);
}
 
void main() {
  var logger1 = Logger();
  var logger2 = Logger();
  print(identical(logger1, logger2));  // true
}

class Point {
  final double x, y;
  
  const Point(this.x, this.y);
}
 
void main() {
  const p1 = Point(1, 2);
  const p2 = Point(1, 2);
  print(identical(p1, p2));  // true
}