How to switch on Enum in Dart?

Question

I'm watching The Boring Flutter Development Show where in one of the episodes they're showing the implementation of Bloc.

Now there's this chunk of code that I thought would be better replace with Switch statement, you know, in case there appears more cases in the future:

_storiesTypeController.stream.listen((storiesType) {
       if (storiesType == StoriesType.newStories) {
         _getArticlesAndUpdate(_newIds);
       } else {
         _getArticlesAndUpdate(_topIds);
       }
     });

... so I tried to implement it but it gave me some error saying that

Type 'Type' of the switch expression isn't assignable to the type 'Stories Type' of case expressions.

So I came up with this workaround:

final storyType = StoriesType.newStories;

_storiesTypeController.stream.listen((storyType) {
    switch (storyType) {
      case StoriesType.newStories: {
        _getArticlesAndUpdate(_newIds);
      }
        break;
      case StoriesType.topStories: {
        _getArticlesAndUpdate(_topIds);
      }
        break;
      default: {
        print('default');
      }
    }
  });

... and everything works fine but I wonder if there's another way to switch Enum and why it says the value of local variable storyType isn't used, when I use it in this line:

_storiesTypeController.stream.listen((storyType)

and I switch over it?

Scabbard

Answer 1

You have a redundant variable that lives in the outer scope:

final storyType = StoriesType.newStories;

Since the callback for _storiesTypeController.stream.listen defines a new variable named storyType, the variable from the outer scope is not used.
You can simply drop the redundant line:

final storyType = StoriesType.newStories;

After you have removed it, there should not be any warnings.
Additionally, you do not need curly braces in a switch-statement. The adjusted code would look like this:

_storiesTypeController.stream.listen((storyType) {
    switch (storyType) {
      case StoriesType.newStories:
        _getArticlesAndUpdate(_newIds);
        break;
      case StoriesType.topStories:
        _getArticlesAndUpdate(_topIds);
        break;
      default:
        print('default');
    }
  });

You can find out more about switch and case in Dart's language tour.

Hwang

Answer 2

Switching on enums is easy, for example:

enum ActivityType {
  running,
  climbing,
  hiking,
  cycling,
  ski
}

extension ActivityTypeNumber on ActivityType {
  int get number {
    switch (this) {
      case ActivityType.running:
        return 1;
      case ActivityType.climbing:
        return 2;
      case ActivityType.hiking:
        return 5;
      case ActivityType.cycling:
        return 7;
      case ActivityType.ski:
        return 10;
    }
  }
}

More on enums and how to use their enhanced version

Christianize

Answer 3

Playing with enum and switch case is easy.

enum PaymentStatus { accepted, declined, unauthorized }

This is the enum on which below switch is working

switch (paymentStatus) {
      case PaymentStatus.accepted:
        postPaymentHandler.handleSuccesFlow();
      case PaymentStatus.declined:
        postPaymentHandler.handleDeclinedError();
      case PaymentStatus.unauthorized:
        postPaymentHandler.handleUnauthorizedError();
      default:
         globalErrorHandler.handleError()
    }

Proparoxytone