How would I represent a compound key in Scala?

Question

If I have

val key1 = "mykey"
val key2 = 427

Is it possible to hash by both? I could do something like

val compoundKey = key1 + "#" + key2
myhash.put(compoundKey, value)

However that seems a bit clunky

Answer 1

Use a Tuple:

val compoundKey = (key1, key2)

Answer 2

I always prefer the new data type over Tuple for three reasons:

case class CompoundKey(key1: String, key2: String)

1. You have a name, especially in compiler warnings and an "expected CompoundKey" is clearer than a "expected Tuple2[String,String]". Or it just helps you with a type annotation to make your own code more readable, especially in nested structures like Maps

   val k: CompoundKey = expensiveComputationOrNonObviousMethodCallsInARow(...)
val keyMap: Map[CompoundKey,Key] instead of Map[(String,String),Key]

2. Access to the subkeys in CompoundKey can be done by name:

   val ckey = CompoundKey("foo","bar")
ckey.key1 instead of ckey._1

3. It lets you change your representation of the nested type, here String, later on. That means if you change String to whatever that you doesn´t have to change Tuple2[String,String] all over your code. Only CompoundKey has to be adapted.

(I even would use a wrapper case class Key(str: String) for the key class)