Step 1 - Products

abstract class TransactionalSender {
  void sendReceipt(String userId, String orderId);
}

abstract class MarketingSender {
  void sendPromo(String userId, String campaign);
}

Step 2 - Abstract factory

abstract class NotificationFamilyFactory {
  TransactionalSender transactional();
  MarketingSender marketing();
}

Step 3 - Dev family

class ConsoleTransactional implements TransactionalSender {
  @override
  void sendReceipt(String userId, String orderId) {
    print('[dev][txn] $userId order $orderId');
  }
}

class ConsoleMarketing implements MarketingSender {
  @override
  void sendPromo(String userId, String campaign) {
    print('[dev][mkt] $userId campaign $campaign');
  }
}

class DevNotificationFactory implements NotificationFamilyFactory {
  @override
  TransactionalSender transactional() => ConsoleTransactional();

  @override
  MarketingSender marketing() => ConsoleMarketing();
}

Step 4 - Prod family (fake)

class HttpTransactional implements TransactionalSender {
  @override
  void sendReceipt(String userId, String orderId) {
    print('[prod][txn] POST receipt $userId $orderId');
  }
}

class HttpMarketing implements MarketingSender {
  @override
  void sendPromo(String userId, String campaign) {
    print('[prod][mkt] POST promo $userId $campaign');
  }
}

class ProdNotificationFactory implements NotificationFamilyFactory {
  @override
  TransactionalSender transactional() => HttpTransactional();

  @override
  MarketingSender marketing() => HttpMarketing();
}

Step 5 - App wiring

NotificationFamilyFactory factoryForEnv(String env) {
  return env == 'prod' ? ProdNotificationFactory() : DevNotificationFactory();
}

void main() {
  final f = factoryForEnv('dev');
  f.transactional().sendReceipt('u1', 'o9');
}

Practice tasks

• Add AuditSender to both families and extend the abstract factory.
• Read one call site that still branches on env; collapse it to receive NotificationFamilyFactory only.
• Contrast Factory method (one product) vs this Abstract factory (product family) in two sentences.