Flutter Example

main.dart

import 'package:flutter/material.dart';

void main() => runApp(
      MaterialApp(
        debugShowCheckedModeBanner: false,
        home: Scaffold(
          body: Center(
            child: FutureBuilder(
              future: Future<String>.delayed(
                  const Duration(seconds: 3), () => 'Hello World!'),
              builder: (context, snapshot) => switch (snapshot) {
                (AsyncSnapshot s) when s.hasData => Text(s.data!),
                (AsyncSnapshot s) when !s.hasError =>
                  const CircularProgressIndicator.adaptive(),
                (_) => const Text('Error'),
              },
            ),
          ),
        ),
      ),
    );