unwrapping-streams-in-dart.dart

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import 'dart:async';

import 'package:flutter/material.dart';
import 'dart:developer' as devtools show log;

extension Log on Object {
  void log() => devtools.log(toString());
}

void main() {
  runApp(
    const App(),
  );
}

extension Unwrap<T> on Stream<T?> {
  Stream<T> unwrap() => where((event) => event != null).cast();
}

int? makeSureIsEven(int value) => value % 2 == 0 ? value : null;

void testIt() async {
  Stream<int?>.periodic(
    const Duration(seconds: 1),
    makeSureIsEven,
  ).unwrap().listen((evenValue) {
    evenValue.log();
  });
}

class App extends StatelessWidget {
  const App({
    Key? key,
  }) : super(key: key);

  @override
  Widget build(BuildContext context) {
    return MaterialApp(
      theme: ThemeData(
        primarySwatch: Colors.blue,
      ),
      debugShowCheckedModeBanner: false,
      home: const HomePage(),
    );
  }
}

class HomePage extends StatelessWidget {
  const HomePage({
    Key? key,
  }) : super(key: key);

  @override
  Widget build(BuildContext context) {
    testIt();
    return Scaffold(
      appBar: AppBar(
        title: const Text('Home Page'),
      ),
    );
  }
}