SortedMap/TreeMap.iterableFactory should explicitly return Seq instead of Iterable

[neontorrent]

reproduction steps

using Scala 2.13.2

scala> collection.mutable.TreeMap(0->0).iterableFactory
val res0: scala.collection.IterableFactory[scala.collection.mutable.Iterable] = scala.collection.mutable.Iterable$@563843f1

scala> collection.immutable.TreeMap(0->0).iterableFactory
val res1: scala.collection.IterableFactory[scala.collection.immutable.Iterable] = scala.collection.immutable.Iterable$@3a988299

problem

Both mutable and immutable TreeMap/SortedMap's iterableFactory return just a normal Iterable. Although it currently works, because IterableFactory is a Delegate of List, it is

• conceptually incorrect. They are sorted in order, and iterableFactory should retain the sequential order. Iterable does not guarrantee the sorted order
• if Iterable implemenetation changes in the future and no longer List, this will break.

Furthermore, currently keySet signature returns a SortedSet, which is accurate, but values returns a simple Iterable. It would be more preferred to return a Seq instead, so the values would also retain the order same as in the SortedMap

[NthPortal]

I'm not sure I agree with the premise here. Seq and Sorted are different properties - the former is insertion order, and the latter follows some Ordering. as evidence, see the existence of both SeqMap and SortedMap. I would agree that iterableFactory for SeqMap probably ought to return an IterableFactory[Seq], however.

[neontorrent]

Seq and Sorted are different properties - the former is insertion order, and the latter follows some Ordering.

Not necessarily. Seq ensures a sequential order. It could be insertion order, order by Ordering, or any non-random order in sequence. (However it does not keep the order if it is modified). My point in this case is, SortedMap iterableFactory should not return an Iterable, because it does not inherit the sorted order as in the SortedMap. For example,

SortedMap("first" -> 2, "second" -> 1).values

return Iterable[Int] (it actually returns List because Iterable uses List as underlying collection). The access order would be (2,1), or (1,2) but in this case I am looking for (2,1) because it is supposed to be sorted by the key and keep that order when I get the values.

[NthPortal]

After thinking about this a bunch, I think I agree. Unfortunately, I don't think it would be binary compatible to add overrides to the traits, so I think you'd have to do it in the individual implementations