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// Discouraged: Mutable setState with force-unwrap and missing const
class BadProfile extends StatefulWidget {
  @override
  _BadProfileState createState() => _BadProfileState();
}
class _BadProfileState extends State<BadProfile> {
  var user;
  void load() async {
    user = await fetchUser();
    setState(() {});
  }
  @override
  Widget build(BuildContext context) {
    return Container(child: Text(user!.name)); // Runtime crash if null!
  }
}

import 'package:flutter/material.dart';
import 'package:flutter_riverpod/flutter_riverpod.dart';

@immutable
sealed class ViewState<T> {
  const ViewState();
}
class Loading<T> extends ViewState<T> { const Loading(); }
class Success<T> extends ViewState<T> { final T data; const Success(this.data); }
class Failure<T> extends ViewState<T> { final String message; const Failure(this.message); }

class ProfileView extends ConsumerWidget {
  const ProfileView({super.key});

  @override
  Widget build(BuildContext context, WidgetRef ref) {
    final state = ref.watch(profileProvider);
    return Scaffold(
      appBar: AppBar(title: const Text('Profile')),
      body: switch (state) {
        Loading() => const Center(child: CircularProgressIndicator.adaptive()),
        Success(:final data) => Center(child: Text('Welcome, ${data.name}')),
        Failure(:final message) => Center(child: Text('Error: $message')),
      },
    );
  }
}