CODESAMPLE

Decorator - Dart

Decorator Dart

The Decorator pattern dynamically adds responsibilities to an object. It provides a flexible alternative to subclassing for extending functionality. Instead of inheriting from a base class to add behavior, we wrap the object in decorator classes that add the desired functionality. This implementation uses Dart’s type system and composition to achieve this. The Component interface defines the core functionality, ConcreteComponent provides a basic implementation, and Decorator extends Component and holds a reference to another Component. Specific behaviors are added by ConcreteDecorator classes, which wrap the component and augment its behavior. This approach is idiomatic Dart as it favors composition over inheritance and leverages Dart’s flexible type system.

// Component interface
abstract class Component {
  String operation();
}

// Concrete Component
class ConcreteComponent implements Component {
  @override
  String operation() => 'Base operation';
}

// Decorator abstract class
abstract class Decorator implements Component {
  final Component _component;

  Decorator(this._component);

  @override
  String operation() => _component.operation();
}

// Concrete Decorator 1
class ConcreteDecoratorA extends Decorator {
  ConcreteDecoratorA(Component component) : super(component);

  @override
  String operation() {
    return 'Decorator A: ' + super.operation();
  }
}

// Concrete Decorator 2
class ConcreteDecoratorB extends Decorator {
  ConcreteDecoratorB(Component component) : super(component);

  @override
  String operation() {
    return 'Decorator B: ' + super.operation();
  }
}

void main() {
  Component component = ConcreteComponent();
  print(component.operation());

  Component decoratorA = ConcreteDecoratorA(component);
  print(decoratorA.operation());

  Component decoratorB = ConcreteDecoratorB(decoratorA);
  print(decoratorB.operation());
}