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

I'm using Flutter to download 3 different sets of data from a server, then do something with all 3 sets. I could do this:

List<Foo> foos = await downloader.getFoos();
List<Bar> bars = await downloader.getBars();
List<FooBars> foobars = await downloader.getFooBars();

processData(foos, bars, foobars);

But I'd prefer to download all 3 data sets asynchronously in parallel. I've seen that Dart has this Future.wait method:

Future<List<T>> wait <T>(
   Iterable<Future<T>> futures, {
   bool eagerError: false, 
   void cleanUp(
      T successValue
   )
}) 

However it looks like this will only return values of the same type (T). I have 3 different types, so I don't see how I can use this and get my 3 data sets back.

What's the best alternative way to achieve this?

Thanks!

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1 Answer

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by (71.8m points)

You need to adapt each of your Future<T>s to a common type of Future. You could use Future<void>:

List<Foo> foos;
List<Bar> bars;
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())(),
]);

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