whereType transformer example

main.dart

import "dart:async";

StreamTransformer<Null, T> whereType<T>() => _WhereTypeTransformer<T>();

class _WhereTypeTransformer<T> extends StreamTransformerBase<Null, T> {
  Stream<T> bind(Stream<Object> stream) async* {
    await for (var value in stream) if (value is T) yield value;
  }
}

Stream<num> get numbers async* {
  yield 1;
  yield 2;
  yield 2.5;
  yield 3;
}

main() async {
  Stream<int> integers = numbers.transform(whereType<int>());
  await integers.forEach(print);
}