Pattern Matching not working on ternary operators

[shinayser]

This code compiles and works properly:

void main() async {
  
  var aIntegerList = [1, 2];  
  
  //It works as expeceted!
  if ( aIntegerList case [1, 2] || [2, 3]) {
    print('Matched!');
  } else {
    print("Didn't matched!");
  }
  
}

But this one doesn't compile:

void main() async {
  
  var aIntegerList = [1, 2];
  
  //It doesn't compile, but why?
  print ( (aIntegerList case [1, 2] || [2, 3])? 'Matched!' : "Didn't matched!" );
  
}

It gives the following error:
Conditions must have a static type of 'bool'.

Dart version: 3.0.5

[vsmenon]

This is working as specified / intended. Case clauses are only supported in certain settings:

https://dart.dev/language/branches#if-case

[vsmenon]

I'll refile this on the language as a feature request.

[shinayser]

Interesting I didn't know.
That sounds pretty non-intuitive for me: if the case returns false for the if why not else on other locations like ternary operators?

[munificent]

if the case returns false for the if why not else on other locations like ternary operators?

When we added patterns, we didn't add a case expression that you happen to be able to use inside an if condition. We added an explicit if (expr case pattern) statement form. That's the only place where you can use case after an expression.

We discussed generalizing that in the initial design, but we didn't have time to work through all of the consequences around precedence and variable scoping.

There is a feature request to support using case in more places: #3059.

[shinayser]

Thanks for the clarification @munificent . Congratulations for your work on that feature. Patter Matching is the thing I am loving most on dart nowadays :)