Kotlin Map none()
Syntax & Examples

Syntax of Map.none()

There are 2 variations for the syntax of Map.none() extension function. They are:

fun <K, V> Map<out K, V>.none(): Boolean

This extension function returns true if the map has no entries.

fun <K, V> Map<out K, V>.none( predicate: (Entry<K, V>) -> Boolean ): Boolean

This extension function returns true if no entries match the given predicate.

✐ Examples

1 Check if map is empty

In this example,

We create a map named map1 containing integer keys and character values.
We then apply the none() function on map1.
As a result, true is returned if the map has no entries.
We print the result to standard output.

Kotlin Program

fun main(args: Array<String>) {
    val map1 = mapOf(1 to 'a', 2 to 'b', 3 to 'c')
    val result = map1.none()
    println(result)
}

Output

false

2 Check if any even values exist in the map

In this example,

We create a map named map2 containing character keys and integer values.
We then apply the none() function on map2 with a predicate checking for even values.
As a result, false is returned if any even values exist in the map.
We print the result to standard output.

Kotlin Program

fun main(args: Array<String>) {
    val map2 = mapOf('a' to 1, 'b' to 2, 'c' to 3)
    val result = map2.none { it.value % 2 == 0 }
    println(result)
}

Output

false

3 Check if any keys are greater than 3 in the map

In this example,

We create a map named map3 containing integer keys and character values.
We then apply the none() function on map3 with a predicate checking for keys greater than 3.
As a result, true is returned if no keys greater than 3 exist in the map.
We print the result to standard output.

Kotlin Program

fun main(args: Array<String>) {
    val map3 = mapOf(1 to 'a', 2 to 'b', 3 to 'c')
    val result = map3.none { it.key > 3 }
    println(result)
}

Output

true

Summary

In this Kotlin tutorial, we learned about none() extension function of Map: the syntax and few working examples with output and detailed explanation for each example.