What is the smartest way to copy a Map in Kotlin?

Use putAll method:

val map = mapOf("1" to 1, "2" to 2)
val copy = hashMapOf<String, Int>()
copy.putAll(map)

Or:

val map = mapOf("1" to 1, "2" to 2)
val copy = map + mapOf<String, Int>() // preset

Your way also looks idiomatic to me.

Just use the HashMap constructor:

val original = hashMapOf(1 to "x")
val copy = HashMap(original)

Update for Kotlin 1.1:

Since Kotlin 1.1, the extension functions Map.toMap and Map.toMutableMap create copies.

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