How can I merge multiple Streams into a higher level Stream?

Question

I have two streams, Stream<A> and Stream<B>. I have a constructor for a type C that takes an A and a B. How do I merge the two Streams into a Stream<C>?

Answer 1

import 'dart:async' show Stream; import 'package:async/async.dart' show StreamGroup;  main() async {   var s1 = stream(10);   var s2 = stream(20);   var s3 = StreamGroup.merge([s1, s2]);   await for(int val in s3) {     print(val);   } }  Stream<int> stream(int min) async* {   int i = min;   while(i < min + 10) {     yield i++;   } } 

See also http://news.dartlang.org/2016/03/unboxing-packages-async-part-2.html

prints

10 20 11 21 12 22 13 23 14 24 15 25 16 26 17 27 18 28 19 29 

Answer 2

You can use StreamZip in package:async to combine two streams into one stream of pairs, then create the C objects from that.

import "package:async" show StreamZip; ... Stream<C> createCs(Stream<A> as, Stream<B> bs) =>   new StreamZip([as, bs]).map((ab) => new C(ab[0], ab[1]));