scala - type mismatch compiler error when concatenating two maps using getOrElse -

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i'm trying concatenate mutable immutable map in scala.

case class result(val key: string, val number: int)  object test extends app {    val map1 = scala.collection.mutable.map[string, list[result]]()   val map2: map[string, list[result]] = map("test" -> list(new result("0", 0)))    map1 ++= map2.map(c => (c -> (c._2 + map1.getorelse(c._1, list[result]()))))  }

but compiler says:

type mismatch;  found   : list[result]  required: string

when change listresult "test" compiler says:

type mismatch;  found   : java.io.serializable  required: string

i'm quite confused. use getorelse wrong way?

regards cyrill

map1 ++= map2.map(c => (c -> (c._2 + map1.getorelse(c._1, list[result]()))))

map on map gets passed each element of map. c (string, list[result]). this

(c -> (c._2 + map1.getorelse(c._1, list[result]()))

is ((string, list[result), (list[result]). wrong. imagine meant

(c._1 -> (c._2 + map1.getorelse(c._1, list[result]()))

but still has type mismatch. think you're hitting common problem of implicit any2string +, , compiler wants string shouldn't.

anyway, 

(c._1 -> (c._2 ++ map1.getorelse(c._1, list[result]()))

seems work

map1 ++= map2.map(c => (c._1 -> (c._2 ++ map1.getorelse(c._1, list[result]()))))

also, nil bit neater:

map1 ++= map2.map(c => (c._1 -> (c._2 ++ map1.getorelse(c._1, nil))))

and clearer again (imo) comprehension

for ((k,v) <-map2) map1 += (k-> (v ++ map1.getorelse(k, nil)))

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