Cached Streamable class

cached_streamable.dart

import 'dart:async';
import 'package:meta/meta.dart';

/// {@template cached_streamable}
/// Extend this class for a streamable, single-data type repository.
/// {@endtemplate}
abstract class CachedStreamable<T> {
  /// {@macro cached_streamable}
  CachedStreamable({
    required T initialState,
    bool broadcast = false,
  })  : _state = initialState,
        _controller =
            broadcast ? StreamController<T>.broadcast() : StreamController<T>();

  /// Currently stored value of the state.
  T _state;

  /// The controller in use.
  final StreamController<T> _controller;

  /// Getter for the state.
  @protected
  T get value => _state;

  /// Setter for the state and adds the value to the controller.
  @protected
  set value(T newValue) {
    if (_state == newValue) return;
    _controller.add(_state = newValue);
  }

  /// Listen to the changes when [value] is updated.
  /// This will yield the currently stored value when listened to and then yield
  /// all future changes to the state.
  Stream<T> get status async* {
    yield _state;
    yield* _controller.stream;
  }

  /// Close controller and clean up the resources used.
  @mustCallSuper
  FutureOr<void> close() => _controller.close();
}

example.dart

import 'dart:async';
import 'cached_streamable.dart';

enum AuthStatus {
  unknown,
  authenticated,
  unauthenticated,
}

class AuthenticationRepository extends CachedStreamable<AuthStatus> {
  AuthenticationRepository() : super(initialState: AuthStatus.unknown);

  Future<void> login({
    required String email,
    required String password,
  }) async {
    await Future<void>.delayed(const Duration(seconds: 2));
    value = AuthStatus.authenticated;
  }

  Future<void> logout() async {
    await Future<void>.delayed(const Duration(seconds: 2));
    value = AuthStatus.unauthenticated;
  }
}

Future<void> main() async {
  final repo = AuthenticationRepository();

  // prints: AuthStatus.unknown
  final subscription = repo.status.listen(print);

  // prints: AuthStatus.authenticated
  await repo.login(
    email: 'email',
    password: 'password',
  );

  // prints: AuthStatus.unauthenticated
  await repo.logout();

  await repo.close();
  await subscription.cancel();
}