Kotlin Tutorials

Kotlin Map toMutableMap()
Syntax & Examples

Syntax of toMutableMap()

The syntax of Map.toMutableMap() extension function is:

fun <K, V> Map<out K, V>.toMutableMap(): MutableMap<K, V>

This toMutableMap() extension function of Map returns a new mutable map containing all key-value pairs from the original map.


✐ Examples

1 Convert to mutable map

In this example,

  • We create a map named map1 containing integer keys and character values.
  • We then apply the toMutableMap() function on map1.
  • As a result, a new mutable map containing all key-value pairs from map1 is returned.
  • 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.toMutableMap()
    println(result)
}

Output

{1=a, 2=b, 3=c}

2 Convert to mutable map

In this example,

  • We create a map named map2 containing character keys and integer values.
  • We then apply the toMutableMap() function on map2.
  • As a result, a new mutable map containing all key-value pairs from map2 is returned.
  • 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.toMutableMap()
    println(result)
}

Output

{a=1, b=2, c=3}

3 Convert to mutable map

In this example,

  • We create a map named map3 containing string keys and integer values.
  • We then apply the toMutableMap() function on map3.
  • As a result, a new mutable map containing all key-value pairs from map3 is returned.
  • We print the result to standard output.

Kotlin Program

fun main(args: Array<String>) {
    val map3 = mapOf("apple" to 1, "banana" to 2, "cherry" to 3)
    val result = map3.toMutableMap()
    println(result)
}

Output

{apple=1, banana=2, cherry=3}

Summary

In this Kotlin tutorial, we learned about toMutableMap() extension function of Map: the syntax and few working examples with output and detailed explanation for each example.