Michal created KAFKA-7301:
-----------------------------
Summary: 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
Reporter: Michal
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 it actually compiles until you try to use
it:)
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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