DartPad Cheatsheet Codelab - 2 - Null-aware operators

hint.txt

All you need to do in this exercise is replace the TODO comments with either ?? or ??=.
Read the codelab text to make sure you understand both, and then give it a try.

main.dart

String foo = 'a string';
String bar; // Unassigned objects are null by default.

// Substitute an operator that makes 'a string' be assigned to baz.
String baz = foo /* TODO */ bar;

void updateSomeVars() {
  // Substitute an operator that makes 'a string' be assigned to bar.
  bar /* TODO */ 'a string';
}

solution.dart

String foo = 'a string';
String bar; // Unassigned objects are null by default.

// Substitute an operator that makes 'a string' be assigned to baz.
String baz = foo ?? bar;

void updateBar() {
  // Substitute an operator that makes 'a string' be assigned to bar.
  bar ??= 'a string';
}

test.dart

void main() {
  final errs = <String>[];
  
  try {
    updateSomeVars();
    
    if (foo != 'a string') {
      errs.add('Looks like foo somehow ended up with the wrong value.');
    } else if (bar != 'a string') {
      errs.add('Looks like bar ended up with the wrong value.');
    } else if (baz != 'a string') {
      errs.add('Looks like baz ended up with the wrong value.');
    }
  } catch (e) {
    errs.add('Tried calling updateSomeVars and received an exception: ${e.runtimeType}.');
  }
  
  if (errs.isEmpty) {
   _result(true);
  } else {
    _result(false, errs);
  }
}