Over a million developers have joined DZone.

Kotlin: The Tuple Type

DZone's Guide to

Kotlin: The Tuple Type

Get your feet wet with Tuples in Kotlin and how to easily define elements, deconstruct constituent types, and a few other tips to help you out.

· Java Zone ·
Free Resource

Bring content to any platform with the open-source BloomReach CMS. Try for free.

It is very easy to write a Tuple type with the expressiveness of Kotlin. My objective, expressed in tests, is the following:

  1. Be able to define a Tuple of up to 5 elements and be able to retrieve the elements using an index like a placeholder in a test expressed with 2 elements, like this:
  2. val tup = Tuple("elem1", "elem2")

  3. Be able to deconstruct the constituent types along the following lines:

  4. val tup = Tuple("elem1", "elem2")
    val (e1, e2) = tup


The implementation for a Tuple of 2 elements is the following in its entirety:

data class Tuple2<out A, out B>(val _1: A, val _2: B)

Kotlin data class provides all the underlying support of being able to retrieve the individual fields and the ability to destructure using an expression like this:

val (e1, e2) = Tuple2("elem1", "elem2")

All I need to do at this point is provide a helper that creates a Tuple of appropriate size based on the number of arguments provided, which I have defined as follows:

object Tuple {
    operator fun <A> invoke(_1: A): Tuple1<A> = Tuple1(_1)
    operator fun <A, B> invoke(_1: A, _2: B): Tuple2<A, B> = Tuple2(_1, _2)
    operator fun <A, B, C> invoke(_1: A, _2: B, _3: C): Tuple3<A, B, C> = Tuple3(_1, _2, _3)
    operator fun <A, B, C, D> invoke(_1: A, _2: B, _3: C, _4: D): Tuple4<A, B, C, D> = Tuple4(_1, _2, _3, _4)
    operator fun <A, B, C, D, E> invoke(_1: A, _2: B, _3: C, _4: D, _5: E): Tuple5<A, B, C, D, E> = Tuple5(_1, _2, _3, _4, _5)

Which allows me to define Tuples of different sizes using a construct that looks like this:

val tup2 = Tuple("elem1", "elem2")
val tup3 = Tuple("elem1", "elem2", "elem3")
val tup4 = Tuple("elem1", "elem2", "elem3", "elem4")

For a little more of a twist, typically a Pair type is an alias for Tuple with 2 elements, and Triple is an alias for a Tuple of 3 elements. This can be trivially defined in Kotlin the following way:

typealias Pair<A, B> = Tuple2<A, B>
typealias Triple<A, B, C> = Tuple3<A, B, C>

Simple indeed! A more filled-in sample is available in my GitHub repo here.

BloomReach CMS: the API-first CMS of the future. Open-source & enterprise-grade. - As a Java developer, you will feel at home using Maven builds and your favorite IDE (e.g. Eclipse or IntelliJ) and continuous integration server (e.g. Jenkins). Manage your Java objects using Spring Framework, write your templates in JSP or Freemarker. Try for free.

java ,kotlin ,tuples

Published at DZone with permission of

Opinions expressed by DZone contributors are their own.

{{ parent.title || parent.header.title}}

{{ parent.tldr }}

{{ parent.urlSource.name }}