Adding orElse function to firstWhere method

Question

I am trying to add the onElse function to the itterator.firstWhere method but I cannot get the syntax right.

I have tried something like

List<String> myList =   String result = myList.firstWhere((o) => o.startsWith('foo'), (o) => null); 

But the compiler has an error of

1 positional arguments expected, but 2 found

I am sure it is a simple syntax problem, but it has me stumped

Answer 1

In case someone came here thanks to google, searching about how to return null if firstWhere found nothing, when your app is Null Safe, use the new method of package:collection called firstWhereOrNull.

import 'package:collection/collection.dart'; // You have to add this manually, for some reason it cannot be added automatically  // somewhere... MyStuff? stuff = someStuffs.firstWhereOrNull((element) => element.id == 'Cat'); 

About the method: https://pub.dev/documentation/collection/latest/collection/IterableExtension/firstWhereOrNull.html

Answer 2

'orElse' is a named optional argument.

void main() {   checkOrElse(['bar', 'bla']);   checkOrElse(['bar', 'bla', 'foo']); }  void checkOrElse(List<String> values) {   String result = values.firstWhere((o) => o.startsWith('foo'), orElse: () => '');    if (result != '') {     print('found: $result');   } else {     print('nothing found');   } }