Creating Pair Instances with mapOf() and to

Kotlin provides several top-level functions for map creation, such as mapOf, which creates a map from a list of Pair instances. The signature of the mapOf function in the Kotlin standard library is as follows:

fun <K, V> mapOf(vararg pairs: Pair<K, V>: Map<K, V>)

Pair is a data class that has two elements named first and second. The signature of the Pair class is as follows:

data class Pair<out A, out B>: Seriallizable The first and second properties of the Pair class correspond to the generic values A and B. While you can create a Pair class using a constructor that takes two arguments, it is more common to use the to function.

@Test
internal fun `create map using to function`() {
    val mapOf = mapOf("a" to 1, "b" to 2, "c" to 2)

    then(mapOf).anySatisfy { key, value ->
        then(key).isIn("a", "b", "c")
        then(value).isIn(1, 2)
    }
}