[KAFKA-1610] Local modifications to collections generated from mapValues will be lost

• Type: Bug
• Status: Patch Available
• Priority: Major
• Resolution: Unresolved
• Labels: newbie
• Assignee: Mayuresh Gharat
• Reporter: Guozhang Wang
• Created: 22/Aug/14 23:28
• Updated: 26/Apr/17 09:04

Description

In our current Scala code base we have 40+ usages of mapValues, however it has an important semantic difference with map, which is that "map" creates a new map collection instance, while "mapValues" just create a map view of the original map, and hence any further value changes to the view will be effectively lost.

Example code:

scala> case class Test(i: Int, var j: Int) {}
defined class Test

scala> val a = collection.mutable.Map(1 -> 1)
a: scala.collection.mutable.Map[Int,Int] = Map(1 -> 1)

scala> val b = a.mapValues(v => Test(v, v))
b: scala.collection.Map[Int,Test] = Map(1 -> Test(1,1))

scala> val c = a.map(v => v._1 -> Test(v._2, v._2))
c: scala.collection.mutable.Map[Int,Test] = Map(1 -> Test(1,1))

scala> b.foreach(kv => kv._2.j = kv._2.j + 1)

scala> b
res1: scala.collection.Map[Int,Test] = Map(1 -> Test(1,1))

scala> c.foreach(kv => kv._2.j = kv._2.j + 1)

scala> c
res3: scala.collection.mutable.Map[Int,Test] = Map(1 -> Test(1,2))

scala> a.put(1,3)
res4: Option[Int] = Some(1)

scala> b
res5: scala.collection.Map[Int,Test] = Map(1 -> Test(3,3))

scala> c
res6: scala.collection.mutable.Map[Int,Test] = Map(1 -> Test(1,2))

We need to go through all these mapValue to see if they should be changed to map

Issue Links

• links to: GitHub Pull Request #2531