Dart Future.wait for multiple futures and get back results of different types

In Dart 3, you should use a Record of Futures instead of a List/Iterable so that you can have heterogeneous types. Dart 3 provides wait extensions for such Records that are similar to Future.wait. (See sudormrfbin’s answer for an example.)

If you must use Future.wait, you need to adapt each of your Future<T>s to a common type of Future. You could use Future<void> and assign the results instead of relying on return values:

late List<Foo> foos;
late List<Bar> bars;
late List<FooBars> foobars;

await Future.wait<void>([
  downloader.getFoos().then((result) => foos = result),
  downloader.getBars().then((result) => bars = result),
  downloader.getFooBars().then((result) => foobars = result),
]);

processData(foos, bars, foobars);

Or if you prefer await to .then(), the Future.wait call could be:

await Future.wait<void>([
  (() async => foos = await downloader.getFoos())(),
  (() async => bars = await downloader.getBars())(),
  (() async => foobars = await downloader.getFooBars())(),
]);