void main() {
  dynamic d = "hello";
  print(d);
  
  d = 1;
  print(d + 1);
}

void main() {
  List array = const [1, 2, 3];
  print(array);
  array.add(4); // ここでダメなはず
  print(array);
}

List array = final [1, 2, 3];

void main() {
  final array = [1, 2, 3];
  print(array);
  array.add(4);
  print(array); 
}

[1, 2, 3]
[1, 2, 3, 4]

class Person {
  String firstName;
  String lastName;

  Person(this.firstName, this.lastName);

  String _member;

  Person.origin() {
    this.firstName = '氏';
    this.lastName = '名';
  }

$ flutter doctor

  ╔════════════════════════════════════════════════════════════════════════════╗
  ║                 Welcome to Flutter! - https://flutter.dev                  ║
  ║                                                                            ║
  ║ The Flutter tool uses Google Analytics to anonymously report feature usage ║
  ║ statistics and basic crash reports. This data is used to help improve      ║
  ║ Flutter tools over time.                                                   ║
  ║                                                                            ║
  ║ Flutter tool analytics are not sent on the very first run. To disable      ║
  ║ reporting, type 'flutter config --no-analytics'. To display the current    ║
  ║ setting, type 'flutter config'. If you opt out of analytics, an opt-out    ║
  ║ event will be sent, and then no further information will be sent by the    ║
  ║ Flutter tool.                                                              ║
  ║                                                                            ║
  ║ By downloading the Flutter SDK, you agree to the Google Terms of Service.  ║
  ║ Note: The Google Privacy Policy describes how data is handled in this      ║
  ║ service.                                                                   ║
  ║                                                                            ║
  ║ Moreover, Flutter includes the Dart SDK, which may send usage metrics and  ║
  ║ crash reports to Google.                                                   ║
  ║                                                                            ║
  ║ Read about data we send with crash reports:                                ║
  ║ https://flutter.dev/docs/reference/crash-reporting                         ║
  ║                                                                            ║
  ║ See Google's privacy policy:                                               ║
  ║ https://policies.google.com/privacy                                        ║
  ╚════════════════════════════════════════════════════════════════════════════╝


Running "flutter pub get" in flutter_tools...                    1,954ms
Doctor summary (to see all details, run flutter doctor -v):
[✓] Flutter (Channel stable, 2.2.0, on macOS 11.2.2 20D80 darwin-x64, locale ja)
[✗] Android toolchain - develop for Android devices
    ✗ Unable to locate Android SDK.
      Install Android Studio from:
      https://developer.android.com/studio/index.html
      On first launch it will assist you in installing the Android SDK
      components.
      (or visit https://flutter.dev/docs/get-started/install/macos#android-setup
      for detailed instructions).
      If the Android SDK has been installed to a custom location, please use
      `flutter config --android-sdk` to update to that location.

[✓] Xcode - develop for iOS and macOS
[✓] Chrome - develop for the web
[!] Android Studio (not installed)
[✓] VS Code (version 1.56.2)
[✓] Connected device (1 available)

! Doctor found issues in 2 categories.

export PATH="$PATH:[PATH_OF_FLUTTER_GIT_DIRECTORY]/bin"

 echo $PATH

$ echo $PATH
/Users/me/.rbenv/shims:/usr/local/bin:/usr/bin:/bin:/usr/sbin:/sbin:/usr/local/share/dotnet:~/.dotnet/tools:/Library/Apple/usr/bin:/Library/Frameworks/Mono.framework/Versions/Current/Commands:/Users/me/Dev/flutter/bin

$ which flutter
/Users/me/Dev/flutter/bin/flutter

open -a simulator

$ flutter config --enable-macos-desktop

$ flutter run -d macos
Launching lib/main.dart on macOS in debug mode...
Exception: No macOS desktop project configured. See
https://flutter.dev/desktop#add-desktop-support-to-an-existing-flutter-app to
learn about adding macOS support to a project.

flutter create --platforms=windows,macos,linux .

$ flutter create --platforms=macos
No option specified for the output directory.
Create a new Flutter project.

If run on a project that already exists, this will repair the project,
recreating any files that are missing.

FAILURE: Build failed with an exception.

* What went wrong:
Could not determine the dependencies of task ':app:compileDebugJavaWithJavac'
  To build this project, accept the SDK license agreements and install the missing components using the Android Studio SDK Manager.
  Alternatively, to transfer the license agreements from one workstation to another, see http://d.android.com/r/studio-ui/export-licenses.html

 Using Android SDK: /Users/xxx/Library/Android/sdk

$ flutter doctor --android-licenses
Exception in thread "main" java.lang.NoClassDefFoundError: javax/xml/bind/annotation/XmlSchema
	at com.android.repository.api.SchemaModule$SchemaModuleVersion.<init>(SchemaModule.java:156)
	at com.android.repository.api.SchemaModule.<init>(SchemaModule.java:75)
	at com.android.sdklib.repository.AndroidSdkHandler.<clinit>(AndroidSdkHandler.java:81)
	at com.android.sdklib.tool.sdkmanager.SdkManagerCli.main(SdkManagerCli.java:73)
	at com.android.sdklib.tool.sdkmanager.SdkManagerCli.main(SdkManagerCli.java:48)
Caused by: java.lang.ClassNotFoundException: javax.xml.bind.annotation.XmlSchema
	at java.base/jdk.internal.loader.BuiltinClassLoader.loadClass(BuiltinClassLoader.java:581)
	at java.base/jdk.internal.loader.ClassLoaders$AppClassLoader.loadClass(ClassLoaders.java:178)
	at java.base/java.lang.ClassLoader.loadClass(ClassLoader.java:522)
	... 5 more

import 'package:flutter/material.dart';

void main() => runApp(MyApp());

class MyApp extends StatelessWidget {
  @override
  Widget build(BuildContext context) {
    return MaterialApp(
      title: 'Welcome to Flutter',
      home: Scaffold(
        appBar: AppBar(
          title: Text('Welcome to Flutter'),
        ),
        body: Center(
          child: Text('Hello World'),
        ),
      ),
    );
  }
}

class WidgetName extends StatefulWidget {
  @override
  _WidgetNameState createState() => _WidgetNameState();
}

class _WidgetNameState extends State<WidgetNameState> {
  @override
  Widget build(BuildContext context) {
    return Container();
  }
}

      setState(() {
        if (alreadySaved) {
          _saved.remove(pair);
        } else { 
          _saved.add(pair); 
        } 
      });

func temp(completion: ((String) -> Void)) {
    completion("temp")
}

temp { message in // (message) in でもよし
    print(message)
}

// 引数を無視することもできる
temp { _ in
    print("aaa")
}

void setState(
    VoidCallback fn
)

setState(() { … })