ch02

list_map_default_function_parameters.dart

doStuff({List<int> list: const[1, 2, 3],
         Map<String, String> gifts: const{'first':  'paper',
                                          'second': 'cotton',
                                          'third':  'leather'}}) {
  print('list:  $list');
  print('gifts: $gifts');
}

main() {
  // Use the default values for both parameters.
  doStuff();

  // Use the default values for the "gifts" parameter.
  doStuff(list:[4,5,6]);
  
  // Don't use the default values for either parameter.
  doStuff(list: null, gifts: null);
}

If you ever need to update to Optional positional parameters in response to this milestone: dart-lang/site-www#180

doStuff([List<int> list = const[1, 2, 3],
         Map<String, String> gifts = const{'first':  'paper',
                                          'second': 'cotton',
                                          'third':  'leather'}]) {
  print('list:  $list');
  print('gifts: $gifts');
}

main() {
  // Use the default values for both parameters.
  doStuff();

  // Use the default values for the "gifts" parameter.
  doStuff([4,5,6]);

  // Don't use the default values for either parameter.
  doStuff(null, null);
}

I've filed dart-lang/site-www#189 about this.