An example of a const class with nested mutable class

const_class_with_nested_mutable.dart

import 'package:flutter/material.dart';

void main() {
  runApp(const MyApp());
}

// global for simplicity
final AleMutableController controller = AleMutableController();

class MyApp extends StatelessWidget {
  const MyApp({super.key});

  @override
  Widget build(BuildContext context) {
    return MaterialApp(
      debugShowCheckedModeBanner: false,
      home: Scaffold(
        body: Center(
          child: const AleConst(),
        ),
        floatingActionButton: FloatingActionButton(
          onPressed: _onPressed,
        ),
      ),
    );
  }

  void _onPressed() {
    controller.mutate();
  }
}

// const class
class AleConst extends StatelessWidget {
  const AleConst();
  @override
  Widget build(final BuildContext context) {
    return AleMutable();
  }
}

// mutable nested class
class AleMutable extends StatelessWidget {
  @override
  Widget build(final BuildContext context) {
    return ListenableBuilder(
      builder: (context, child) => Text(controller.state),
      listenable: controller,
    );
  }
}

class AleMutableController extends ChangeNotifier {
  String _state = 'ale';
  String get state => _state;

  void mutate() {
    final newState = _state == 'ale' ? 'mike' : 'ale';
    _state = newState;
    notifyListeners();
  }
}