Why, in the below code example, does isAList
's for
comprehension yield a List, but the other two yield Maps? I can't think of any reason - the only difference seems to be that there is isAList
's comprehension declares two variables, and the others declare one or zero.
object Weird {
def theMap: Map[Int, String] =
Map(1 -> "uno", 2 -> "dos", 3 -> "tres")
def main(args: Array[String]) {
val isAMap = for {
(key, value) <- theMap
} yield (key*2 -> value*2)
val isAlsoAMap = for {
(key, value) <- theMap
doubleKey = key*2
} yield (doubleKey -> value*2)
val isAList = for {
(key, value) <- theMap
doubleKey = key*2
doubleValue = value*2
} yield (doubleKey -> doubleValue)
println(isAMap)
println(isAlsoAMap)
println(isAList)
}
}
outputs
Map(2 -> unouno, 4 -> dosdos, 6 -> trestres)
Map(2 -> unouno, 4 -> dosdos, 6 -> trestres)
List((2,unouno), (4,dosdos), (6,trestres))
I am comparatively new to Scala, so apologies if I'm being incredibly naive about something!
scalac -print
to see the de-sugared program.