combine.kt

@PublishedApi
internal object UnInitialized

@PublishedApi
internal inline fun <T, R> combine(vararg sources: Flow<T>, crossinline transform: suspend (List<T>) -> R): Flow<R> {
  return channelFlow {
    val values = Array<Any?>(sources.size) { UnInitialized }
    coroutineScope {
      sources.mapIndexed { index, flow ->
        launch {
          flow.collect { value ->
            values[index] = value
            if (values.all { it !== UnInitialized }) {
              send(transform(values.toList() as List<T>))
            }
          }
        }
      }.joinAll()
    }
  }
}