What is _CompactLinkedHashSet in flutter? - flutter

Question

I am trying to run my first flutter app and I am getting a redscreen error when I run it on my iPhone but it runs without a problem on the simulator:
type '_CompactLinkedHashSet' is not a subtype of type 'Widget'.
Does anyone know what this error refers to? The error-causing widget is a FutureBuilder. The type of the FutureBuilder is the same as the Future.
Flutter doctor:
[✓] Flutter (Channel dev, v1.18.0, on Mac OS X 10.15.4 19E287, locale en-AU)
• Flutter version 1.18.0 at /Users/Josh/Developer/flutter
• Framework revision 8f7327f83a (11 days ago), 2020-04-06 22:11:01 -0400
• Engine revision 49891e0653
• Dart version 2.8.0 (build 2.8.0-dev.20.0 1210d27678)
[✓] Android toolchain - develop for Android devices (Android SDK version 29.0.3)
• Android SDK at /Users/Josh/Library/Android/sdk
• Platform android-29, build-tools 29.0.3
• Java binary at: /Applications/Android Studio.app/Contents/jre/jdk/Contents/Home/bin/java
• Java version OpenJDK Runtime Environment (build 1.8.0_212-release-1586-b4-5784211)
• All Android licenses accepted.
[✓] Xcode - develop for iOS and macOS (Xcode 11.4.1)
• Xcode at /Applications/Xcode.app/Contents/Developer
• Xcode 11.4.1, Build version 11E503a
• CocoaPods version 1.9.1
[✓] Android Studio (version 3.6)
• Android Studio at /Applications/Android Studio.app/Contents
• Flutter plugin version 45.1.1
• Dart plugin version 192.7761
• Java version OpenJDK Runtime Environment (build 1.8.0_212-release-1586-b4-5784211)
[!] Connected device
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! Doctor found issues in 1 category.
class DisclaimerData {
bool agreed;
String version;
DisclaimerData({this.agreed, this.version});
}
class DisclaimerView extends StatefulWidget {
#override
_DisclaimerViewState createState() => _DisclaimerViewState();
}
class _DisclaimerViewState extends State<DisclaimerView> {
Future<DisclaimerData> _getAgreed() async {
final preferences = await SharedPreferences.getInstance();
final disclaimerValues = DisclaimerData();
disclaimerValues.agreed = preferences.getBool('disclaimer_agreed') ?? false;
disclaimerValues.version =
preferences.getString('disclaimer_version') ?? '0';
return disclaimerValues;
}
#override
Widget build(BuildContext context) {
return FutureBuilder<DisclaimerData>(
future: _getAgreed(),
builder: (context, snapshot) {
if (snapshot.hasData) {
return Scaffold(
...

Answer 1

_CompactLinkedHashSet is an alternative name for Set. It is internal default Set implementation that dart uses to optimize Set's data structure.
_CompactLinkedHashSet (default Set implementation) and _InternalLinkedHashMap (default Map) have good asymptotic storage efficiency as the size of the collection grows. They are always better than conveniently available alternatives above 10 elements and are designed for a better locality.
source:
https://github.com/dart-lang/sdk/issues/26081