Why no mutable sorted map in Scala

Question

I have been looking for options to implement a mutable sorted map in scala. I know I can store my data in a mutable map and then transformed into a sorted map if is needed or wrap the TreeMap from Java. However, Does anyone know why this is not implemented in scala? Is against any functional programming style?

Regards

The 2 keys concepts of functionnal programming are 'function are objects' and 'immutability' — Arnaud Denoyelle, Sep 05 '16 at 16:11
then, the best implementation should be to have a mutable map and then transform this map to a new one by sorting it. ? — ypriverol, Sep 05 '16 at 16:16
However, @Jasper-M scala has mutable collections mutable.Map, etc. — ypriverol, Sep 05 '16 at 16:18
Looks like it's implemented in 2.12: https://github.com/scala/scala/blob/v2.12.0-M4/src/library/scala/collection/mutable/TreeMap.scala — Victor Moroz, Sep 05 '16 at 16:51

score 5 · Accepted Answer · answered Sep 05 '16 at 21:05

5

There is no reason but the omission of writing one. In fact, a mutable sorted map was added to Scala 2.12.x.

answered Sep 05 '16 at 21:05

sjrd

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score 1 · Answer 2 · edited May 23 '17 at 11:51

There's some discussion in this old answer about possible reasons there isn't an implementation.

With regards to your second question, there are other mutable collections in Scala so I don't see any hard reason there couldn't be a mutable sorted map (see the older question as well). In a more general sense, functional programming can be taken to imply that mutable data is not used, and in this case a mutable sorted map would be avoided. However mutable collections may well be used "behind the scenes" in a library to improve performance, as long as they won't be visible to users of the library.

Why no mutable sorted map in Scala

2 Answers2