CODEWITHSUNDEEP
dartswitch-statement
Joel Broström
Joel Broström

Reputation: 4060

Can I use 'is' operator in a switch case in Dart?

I feel like this is a stupid question, but I cant get it to work.

What I have:

if (current is classA){
   //do stuff
   return;
}
if (current is classB){
   //do stuff
   return;
}
if (current is classC){
   //do stuff
   return;
}

What I want:

switch (currentState) {
   case is classA: { 
      //do stuff
      break;
   }
   case is classB: { 
      //do stuff
      break;
   }
   case is classC: { 
      //do stuff
      break;
   }
}

What I really want (Kotlin):

When (currentState){
   is classA -> //do stuff
   is classB -> //do stuff
   is classC -> //do stuff
}

Is there anyway I can use the Dart Switch like the Kotlins When operator, or at least use other operators then == to assert the case evaluations?

Upvotes: 12

Views: 5706

Answers (3)

lrn
lrn

Reputation: 71693

Edit: Yes, now you can. Dart 3.0 introduced pattern matching, so now you can write:

switch (currentState) {
  case classA():
      //do stuff
  case classB():
      //do stuff
  case classC():
      //do stuff
}

You can also do much more, read about it here: https://dart.dev/language/patterns

The historical answer was:

No.

The Dart switch case is a very low-level construct. It allows only constant-value expressions that don't override operator == (except for a few basic platform types), so effectively it can be implemented using identical checks.

There is no ability to do complicated checks, or checks on the type of the object, only identity checks.

The recommended pretty way to do what you want is to have ClassA, > ClassB and ClassC all implement an interface with a doStuff member, and then do:

currentState.doStuff()

If that is not possible, you are back to the if sequence.

Upvotes: 10

Andrey Molochko
Andrey Molochko

Reputation: 768

switch (runtimeType) {
   case ClassA: //do stuff 
      return;
   case ClassB: //do stuff
      return;
}

Upvotes: 6

Rafa0809
Rafa0809

Reputation: 1752

You can't use the same syntax as in Kotlin but you can use Freezed.

https://pub.dev/packages/freezed

It allows you to use a similar syntax.

Considering this model:

@freezed
abstract class Model with _$Model {
  factory Model.first(String a) = First;
  factory Model.second(int b, bool c) = Second;
}

You can use when in the following way:

var model = Model.first('42');

print(
  model.when(
    first: (String a) => 'first $a',
    second: (int b, bool c) => 'second $b $c'
  ),
); // first 42

Upvotes: 5

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