How can I have a composite key in Kotlin?

Question

In Python i can have complex dictionary keys like for example:

d = {}
d[(1, 2)] = 3
print d[(1, 2)]  # prints 3

How can I declare and populate such a Map in Kotlin?

Edit: I tried to declare a Map like this, but I don't know how to populate it:

val my_map = HashMap<Pair<Int, Int>, Int>()

Answer 1

It's simple, you first create your dictionary and then insert the key and values:

val (a, b):Pair<Int, String> = Pair(1, "x")

val map: HashMap<Pair<Int, String>, Int> = hashMapOf((a, b) to 1)

map[Pair(2, "y")] = 3

and so on :)

Answer 2

In Kotlin, unlike Python there's no tuple data type. For two-tuples there's a Pair class. For larger arity you are supposed to use data classes.

val map: HashMap<Pair<Int, Int>, Int> = hashMapOf(Pair(1, 2) to 3)
val nullable: Int? = map[Pair(1, 2)]
val notNullable = map.getValue(Pair(1, 2))