Async where and examples for List<T>

main.dart

void main(List<String> arguments) async {
  var list = List.generate(10, (i) => i)..addAll(List.generate(10, (i) => i));
  //Normal Where
  print(list.where(foo).toList());
  //Async Where
  print((await list.whereAsync(fooAsync)).toList());
  //Normal UniqueWhere
  print(list.uniqueWhere(foo).toList());
  //Async UniqueWhere
  print((await list.uniqueWhereAsync(fooAsync)).toList());
}

bool foo(int n) {
  return n > 5;
}

Future<bool> fooAsync(int n) async {
  await Future.delayed(Duration(seconds: 1));
  return foo(n);
}

extension MyIterable<T> on Iterable<T> {
  Future<Iterable<T>> whereAsync(Future<bool> Function(T) test) async {
    return (await Future.wait(
      map((e) async {
        return [await test(e), e];
      }),
    ))
        .where((t) => t.first)
        .map((t) => t.last);
  }

  Iterable<T> uniqueWhere(bool Function(T) test) {
    return Set.from(where(test));
  }

  Future<Iterable<T>> uniqueWhereAsync(Future<bool> Function(T) test) async {
    return Set.from(await whereAsync(test));
  }
}