mdedetrich commented on code in PR #1422:
URL: https://github.com/apache/pekko/pull/1422#discussion_r1703180929
##########
stream/src/main/scala/org/apache/pekko/stream/scaladsl/Flow.scala:
##########
@@ -428,6 +428,57 @@ object Flow {
*/
def fromFunction[A, B](f: A => B): Flow[A, B, NotUsed] = apply[A].map(f)
+ /**
+ * Creates a FlowW from an existing base Flow outputting an optional element
and
+ * applying an additional viaFlow only if the element in the stream is
defined.
+ *
+ * '''Emits when''' the provided viaFlow is runs with defined elements
+ *
+ * '''Backpressures when''' the viaFlow runs for the defined elements and
downstream backpressures
+ *
+ * '''Completes when''' upstream completes
+ *
+ * '''Cancels when''' downstream cancels
+ *
+ * @param flow The base flow that outputs an optional element
+ * @param viaFlow The flow that gets used if the optional element in is
defined.
+ * @param combine How to combine the materialized values of flow and viaFlow
+ * @return a Flow with the viaFlow applied onto defined elements of the
flow. The output value
+ * is contained within an Option which indicates whether the
original flow's element had viaFlow
+ * applied.
+ * @since 1.1.0
+ */
+ def optionalVia[FIn, FOut, FViaOut, FMat, FViaMat, Mat](flow: Flow[FIn,
Option[FOut], FMat],
Review Comment:
The optional is necessary for the problem I am solving since
1. I need to keep the elements that don't fulfill the predicate (i.e. I am
using `StreamWithContext`/`FlowWithContext` and I don't want to lose the
context)
2. I want to know which elements were filtered and which weren't after the
matter of fact, so even if this was changed to a predicate it wouldn't
ultimately save on performance as I would manually have to add the
functionality to achieve this.
I am not against adding an alternative version that avoids boxing due to
using a predicate but I would suggest to do that in a different PR, and as
@raboof pointed out earlier that may not even need a specific utility function
depending on whether point 2 is important or not.
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