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:

val aMap =   Map(key1 -> value1,       key2 -> value2,       (if (condition) (key3 -> value3) else ???)) 

How can this be done without using a var? What should replace the ???? Is it better to use the + operator?

val aMap =   Map(key1 -> value1,       key2 -> value2) +   (if (condition) (key3 -> value3) else ???)) 

One possible solution is:

val aMap =   Map(key1 -> value1,       key2 -> value2,       (if (condition) (key3 -> value3) else (null, null))).filter {         case (k, v) => k != null && v != null       } 

Is this the best way?

Answer 1

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:_*) 

Answer 2

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)