builder_class_improved.dart

class SomeBuilder extends StatelessWidget {
  @override
  Widget build(BuildContext context) {
    return Builder(
      builder: (innerContext) {
        return NewIconButton();
      },
    );
  }
}

class NewIconButton extends StatelessWidget {
  @override
  Widget build(BuildContext context) {
    return IconButton(
      onPressed: () {
        final theme = Theme.of(context);
        ...,
      },
    );
  }
}