Question for instantiating of Seq

Question
#1 
scala> val xx = Set(1,2,3)
val xx: scala.collection.immutable.Set[Int] = Set(1, 2, 3)

scala> val yy = Seq(1,2,3)
val yy: Seq[Int] = List(1, 2, 3)

scala> val zz = Map(1 -> 2, 3 -> 4)
val zz: scala.collection.immutable.Map[Int,Int] = Map(1 -> 2, 3 -> 4)

As you see above, only Seq is instantiated as List.
But Map not instantiated as HashMap, Set not instantiated as HashSet.
Why this happens? Thanks.

#2

If you look at the class of the created map you’ll notice that it is in fact scala.collection.immutable.Map$Map2 in this case. This is because immutable maps of 0, 1, 2, 3 and 4 elements all have their own special implementation. As for the output stating it as scala.collection.immutable.Map[Int,Int], this is caused by Map2 inheriting scala.collection.Map.stringPrefix (which sets it to Map).

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