Using Pair and Triple

What are tuples?

Tuples are sequences of objects of small, finite size. Unlike some languages that provide a way to create tuples of different sizes, Kotlin provides two specific types: Pair for a tuple of size two and Triple for a size of three. Use these two when you want to quickly create two or three objects as a collection.

The Pair tuple

Here’s an example of creating a Pair of Strings:

println(Pair("Tom", "Jerry")) //(Tom, Jerry)
println(mapOf("Tom" to "Cat", "Jerry" to "Mouse")) //{Tom=Cat, Jerry=Mouse}

First we create an instance of Pair using the constructor. Then we use the to() extension function, that’s available on any object in Kotlin, to create pairs of entries for a Map. The to() method creates an instance of Pair, with the target value as the first value in the Pair and the argument provided as the second value in the Pair.

The ability to create a pair of objects with such concise syntax is useful. The need to work with a pair of objects is common in programming. For example, if you have a list of airport codes and want to get the temperature at each of these airports, then representing the airport code and temperature as a pair of values is natural. In Java, if you hold the values in an array, it’ll get cumbersome to work with. Besides, we’ll lose type safety since airport code is a String and temperature is a double, and the array will end up being of type Object—smelly. In Java we normally create a specialized class to hold the two values. This approach will provide type safety and remove some noise in code, but it increases the burden on us to create a separate class just for this purpose. Java provides no pleasant way to deal with this. Kotlin Pair solves the issue elegantly.

To see the benefit of Pair, let’s create an example to collect the temperature values for different airport codes.