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Asked: 2026-05-17T21:54:01+00:00

Why is there a lack of consistency between Sets and Lists in Scala Collections

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Why is there a lack of consistency between Sets and Lists in Scala Collections API?

For example, there is immutable Set, but also a mutable one. If I want to use the latter, I can simply do this:

val set = Set[A]()
set += new A

However, there is no mutable List, per se. If I want to write a similar code snippet using Lists, which data structure to use? LinkedList sounds as a good candidate, because it is mutable, but has no += method defined. ListBuffer seems to satisfy the requirements, but it is not a list.

After reading 2.8 Collections docs I come to the conclusion MutableList is probably the best fit.

I still somehow wish there was scala.collection.mutable.List.

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1 Answer

  1. Editorial Team

    The reason for this is that Java has co-opted the functional List type to mean something that it is not (i.e. java.util.List is not a list).

    It probably makes no sense for a functional programming language to have a mutable List as such a type is an oxymoron. Hence ListBuffer or ArrayBuffer. Or just use IndexedSeq, of which there are mutable and immutable implementations

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