Flutter Statelessful widget (inline stateful widgets)

statelessful.dart

import 'package:flutter/material.dart';

class Statelessful<T> extends StatefulWidget {
  final T Function() initialState;
  final Widget Function(
    BuildContext context,
    T state,
    void Function(T state) setState,
  ) builder;

  Statelessful({
    Key key,
    @required this.builder,
    @required this.initialState,
  })  : assert(builder != null),
        assert(initialState != null),
        super(key: key);

  @override
  _StatelessfulState<T> createState() => _StatelessfulState<T>();
}

class _StatelessfulState<T> extends State<Statelessful<T>> {
  T _state;

  void _setState(T state) {
    if (state != _state) {
      setState(() {
        _state = state;
      });
    }
  }

  @override
  void initState() {
    super.initState();

    _state = widget.initialState();
  }

  @override
  Widget build(BuildContext context) {
    return widget.builder(context, _state, _setState) ?? Container();
  }
}