Good morning, is there an operator for concatenati...

# coroutines

[svenjacobs]

Good morning, is there an operator for concatenating two `Flow`s, something like:

val flow1 = flowOf(1, 2, 3)
val flow2 = flowOf(4, 5, 6)
val flow3 = flow1.concat(flow2) // = 1, 2, 3, 4, 5, 6

The order of flow3 does not matter here, so it also might be 1, 4, 2, 5, 3, 6 or any other order, depending on how the values are produced in flow1 and flow2.

[svenjacobs]

val flow3 = flow {
  flow1.collect { emit(it) }
  flow2.collect { emit(it) }
}

is a solution but I'm wondering if there is a simpler solution 😉

[louiscad]

flatMapConcat

[svenjacobs]

I'm not sure this is the operator I'm looking for, since the returned Flow in the transform function will be applied to any value of flow1. So if I call flow1.flatMapConcat { flow2 } the result will be 4, 5, 6, 4, 5, 6, 4, 5, 6

[svenjacobs]

So to be clear, every value of flow1 and flow2 should only be there once in the resulting flow 😉

[marstran]

You could do flowOf(flow1, flow2).flattenConcat()

[svenjacobs]

Thanks @marstran, this is what I was looking for

[svenjacobs]

Hm, unfortunately still not really what I need because this is sequential. I mean this works in my example code but what if flow1 for instance needs 5 seconds before producing the first value but flow2 is faster? Then the first results will still be collected once flow1 has produced it's values. Also what if any of the flows are not terminal?

[marstran]

If you want to merge them instead, you can use flattenMerge().