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https://issues.apache.org/jira/browse/KAFKA-7301?page=com.atlassian.jira.plugin.system.issuetabpanels:all-tabpanel
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Guozhang Wang resolved KAFKA-7301.
----------------------------------
Resolution: Fixed
Fix Version/s: 2.1.0
> KTable to KTable join invocation does not resolve in Scala DSL
> --------------------------------------------------------------
>
> Key: KAFKA-7301
> URL: https://issues.apache.org/jira/browse/KAFKA-7301
> Project: Kafka
> Issue Type: Bug
> Components: streams
> Affects Versions: 2.0.0
> Reporter: Michal
> Priority: Major
> Labels: scala
> Fix For: 2.1.0
>
>
> I found a peculiar problem while doing KTable to KTable join using Scala DSL.
> The following code:
>
> {code:java}
> val t1: KTable[String, Int] = ...
> val t2: KTable[String, Int] = ...
> val result = t1.join(t2)((x: Int, y: Int) => x + y)
> {code}
>
> does not compile with "ambiguous reference to overloaded function".
> A quick look at the code shows the join functions are defined as follows:
>
> {code:java}
> def join[VO, VR](other: KTable[K, VO])(
> joiner: (V, VO) => VR,
> materialized: Materialized[K, VR, ByteArrayKeyValueStore]
> )
> def join[VO, VR](other: KTable[K, VO])(joiner: (V, VO) => VR)
> {code}
>
> the reason it does not compile is the fact that the first parameter list is
> identical. For some peculiar reason the KTable class actually compiles...
> The same problem exists for KTable to KTable leftJoin. Other joins
> (stream-stream, stream-table) do not seem to be affected as there are no
> overloaded versions of the functions.
> This can be reproduced in smaller scale by some simple scala code:
>
> {code:java}
> object F {
> //def x(a: Int): Int = 5
> //def x(a: Int): Int = 6 //obviously does not compile
> def f(x: Int)(y: Int): Int = x
> def f(x: Int)(y: Int, z: Int): Int = x
> }
> val r = F.f(5)(4) //Cannot resolve
> val r2 = F.f(5)(4, 6) //cannot resolve
> val partial = F.f(5) _ //cannot resolve
> /* you get following error:
> Error: ambiguous reference to overloaded definition,
> both method f in object F of type (x: Int)(y: Int, z: Int)Int
> and method f in object F of type (x: Int)(y: Int)Int
> match argument types (Int)
> */{code}
>
> The solution: get rid of the multiple parameter lists. I fail to see what
> practical purpose they serve anyways. I am happy to supply appropriate PR if
> there is agreement.
>
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