In Java, I use LinkedHashMap for this purpose. The documentation of Java's LinkedHashMap is very clear that it has "predictable iteration order" and I need the same in Scala.
Scala has ListMap and LinkedHashMap, but the documentation on what they do exactly is poor.
Question: Is Scala's LinkedHashMap or ListMap the implementation to use for this purpose? If not, what other options are available besides using the Java's LinkedHashMap directly?
Scala 2.13 is introducing two new immutable implementations of Map which keep insertion order: VectorMap and SeqMap. See this PR:
Currently there isn't any known immutable map which also maintains key insertion order while keeping effectively constant lookup time on key, so the only known implementations are done by combining a Vector with a HasMap (or in Scala's case HashMap/ChampHashMap)
As of writing, Scala 2.13 is still scheduled to be released in 2018.
UPDATE 2021-04-14: Scala 3.13 does have VectorMap now. SeqMap is just a "generic trait for ordered immutable maps". Besides the new VectorMap and the older ListMap, there is also a new TreeSeqMap.
Note that mutable.ListMap got deprecated with 2.13, but immutable.ListMap is still current.
