generic.dart

import 'package:flutter/material.dart';

typedef Widget FormWidgetBuilder<T>(T t);

class GenericShizzle<T> extends StatefulWidget {
  final FormWidgetBuilder<T> builder;

  const GenericShizzle({
    this.builder,
  });

  @override
  GenericShizzleState<T> createState() {
    return GenericShizzleState<T>();
  }
}

class GenericShizzleState<T> extends State<GenericShizzle<T>> {

  
  @override
  Widget build(BuildContext context) {
    return Text(
        "my builder is of type:" + widget.builder.runtimeType.toString());
  }
}

void main() {
  runApp(
    MaterialApp(
      home: Scaffold(
        body: Center(
          child: GenericShizzle(
            builder: (int i) => Text(i.toString()),
          ),
        ),
      ),
    ),
  );
}