What are cases used for in Flutter?

Use cases represent a layer of business logic separated from the UI and data. They describe specific actions performed by the user or system that operate on data retrieved from repositories.

Advantages of using use cases:

• Cleanliness and modularity: Separating business rules from the UI makes the code more understandable and easier to maintain.
• Testability: Business logic encapsulated in use cases is easy to test in isolation.
• Reusability: Use cases can be used in different parts of the application or even in other applications.
• Readability: Use case names often reflect the intent of the user or system, improving code readability.

Typically, use cases:

• Depend on one or more repositories to fetch data.
• Perform operations on this data (e.g., filtering, sorting, transforming).
• Are unaware of the UI and do not interact with it directly.
• Are used by presenters or state providers (e.g., BLoC, Riverpod).

Example of a use case structure:

// Abstract base class for use cases that return future values.
abstract class FutureUseCase<T, P> {
  Future<T> call(P params);
}

// Specific use case for retrieving a list of users.
class GetUsersUseCase extends FutureUseCase<List<User>, NoParams> {
  final UserRepository userRepository;

  GetUsersUseCase(this.userRepository);

  @override
  Future<List<User>> call(NoParams params) async {
    return await userRepository.getUsers();
  }
}

// Class without parameters for use cases that do not require input data.
class NoParams {}