Hands-On Design Patterns with Kotlin

Tuples

In functional programming, a tuple is a piece of data that cannot be changed after it is created. One of the most basic tuples in Kotlin is Pair:

val pair = "a" to 1

Pair contains two properties, first and second, and is immutable:

pair.first = "b" // Doesn't workpair.second = 2  // Still doesn't

We can destructure a Pair into two separate values:

val (key, value) = pairprintln("$key => $value")

When iterating over a map, we receive another tuple, Map.Entry:

for (p in mapOf(1 to "Sunday", 2 to "Monday")) {   println("${p.key} ${p.value}")}

In general, data classes are usually a good implementation for tuples. But, as we'll see in the Value Mutation section, not every data class is a proper tuple.