Optionally adding items to a Scala Map

Question

I am looking for an idiomatic solution to this problem.

I am building a val Scala (immutable) Map and would like to optionally add one or more items:

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Answer 1

Another possibility is to take advantage of the iterable nature of Option.

A non-empty value o:

scala> val o = Some('z' -> 3)
scala> (Seq('x' -> 1, 'y' -> 2) ++ o).toMap
res1: scala.collection.immutable.Map[Char,Int] = Map(x -> 1, y -> 2, z -> 3)

An empty value o:

scala> val o = None
scala> (Seq('x' -> 1, 'y' -> 2) ++ o).toMap
res2: scala.collection.immutable.Map[Char,Int] = Map(x -> 1, y -> 2)

Answer 2

You can add directly to the map:

scala> val map = Map(1 -> 2, 3 -> 4)
scala> val some = Some(5 -> 6)
scala> val none = None
scala> val combinedMap = map ++ some ++ none
combinedMap: scala.collection.immutable.Map[Int,Int] = Map(1 -> 2, 3 -> 4, 5 -> 6)

Answer 3

How about something along the lines of

val optional = if(condition) Seq((key3 -> value3)) else Nil
val entities = Seq(key1 -> value1, key2 -> value2) ++ optional
val aMap = Map(entities:_*)