Defines an interface for creating an object, but lets subclasses decide which class to instantiate.

Unlike Abstract Factory, it focuses on a single product rather than families of products.

abstract class Notification {
  void send(String message);
}

class EmailNotification implements Notification {
  @override
  void send(String message) => print('Email: $message');
}

class SmsNotification implements Notification {
  @override
  void send(String message) => print('SMS: $message');
}

class NotificationFactory {
  static Notification create(String type) => switch (type) {
    'email' => EmailNotification(),
    'sms' => SmsNotification(),
    _ => throw ArgumentError('Unknown type: $type'),
  };
}

// Usage
NotificationFactory.create('email').send('Hello!');