Cascade Notation (..) trong Dart

class Person {
  String name = '';
  int age = 0;
  String city = '';
  
  void introduce() {
    print('$name, $age, from $city');
  }
}
 
void main() {
  // Không dùng cascade
  var person1 = Person();
  person1.name = 'Alice';
  person1.age = 25;
  person1.city = 'Hanoi';
  
  // Dùng cascade
  var person2 = Person()
    ..name = 'Bob'
    ..age = 30
    ..city = 'HCMC'
    ..introduce();
}

class StringBuilder {
  final StringBuffer _buffer = StringBuffer();
  
  void append(String s) => _buffer.write(s);
  void appendLine(String s) => _buffer.writeln(s);
  void clear() => _buffer.clear();
  
  @override
  String toString() => _buffer.toString();
}
 
void main() {
  var sb = StringBuilder()
    ..append('Hello ')
    ..append('World')
    ..appendLine('!')
    ..appendLine('How are you?');
  
  print(sb);
}

void main() {
  var numbers = <int>[]
    ..add(1)
    ..add(2)
    ..add(3)
    ..addAll([4, 5, 6])
    ..remove(3)
    ..sort();
  
  print(numbers);  // [1, 2, 4, 5, 6]
}

void main() {
  var user = <String, dynamic>{}
    ..['name'] = 'Alice'
    ..['age'] = 25
    ..['email'] = 'alice@email.com'
    ..remove('email');
  
  print(user);  // {name: Alice, age: 25}
}

class Config {
  String? host;
  int? port;
}
 
void main() {
  Config? config;
  
  // Không làm gì nếu null
  config
    ?..host = 'localhost'
    ..port = 8080;
  
  print(config);  // null
}

class Button {
  String text = '';
  String color = 'blue';
  bool enabled = true;
  VoidCallback? onPressed;
  
  Button(this.text);
}
 
void main() {
  var button = Button('Submit')
    ..color = 'green'
    ..enabled = true
    ..onPressed = () => print('Clicked!');
}

class Address {
  String street = '';
  String city = '';
}
 
class Person {
  String name = '';
  Address address = Address();
}
 
void main() {
  var person = Person()
    ..name = 'Alice'
    ..address = (Address()
      ..street = '123 Main St'
      ..city = 'Hanoi');
}

// Builder Pattern truyền thống
class PersonBuilder {
  String _name = '';
  int _age = 0;
  
  PersonBuilder name(String n) {
    _name = n;
    return this;
  }
  
  PersonBuilder age(int a) {
    _age = a;
    return this;
  }
  
  Person build() => Person(_name, _age);
}
 
// Với cascade - không cần builder
var person = Person()
  ..name = 'Alice'
  ..age = 25;

void main() {
  // Cascade trả về object gốc
  var list = [3, 1, 2]..sort();
  print(list);  // [1, 2, 3]
  
  // Khác với method return
  var sorted = [3, 1, 2].toList()..sort();
  print(sorted);  // [1, 2, 3]
}