Clone a map in Kotlin

This article explores different ways to clone a map in Kotlin. The solution should create a copy of all the mappings from the given map to the new map.

1. Using `toMap()` function

You can use the native methods toMap() and toMutableMap() to return a copy of a map. The toMap() function returns an immutable instance of the map, while toMutableMap() function returns a mutable instance.

fun main() {

val map: Map<Int, String> = mutableMapOf(1 to "one", 2 to "two", 3 to "three")

val clone: Map<Int, String> = map.toMutableMap()

println(clone) // {1=one, 2=two, 3=three}

}

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2. Using Copy Constructor

Another simple and fairly efficient solution is to use the HashMap‘s copy constructor, which creates a new map as a copy of an existing map.

fun main() {

val map: Map<Int, String> = mutableMapOf(1 to "one", 2 to "two", 3 to "three")

val clone: Map<Int, String> = HashMap(map)

println(clone) // {1=one, 2=two, 3=three}

}

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3. Using `putAll()` function

Alternatively, you can also use the putAll() function to copy all mappings from the original map to an empty map.

fun <K, V> clone(original: Map<K, V>): MutableMap<K, V> {

val copy: MutableMap<K, V> = HashMap()

copy.putAll(original)

return copy

}

fun main() {

val map: Map<Int, String> = mutableMapOf(1 to "one", 2 to "two", 3 to "three")

val clone: Map<Int, String> = clone(map)

println(clone) // {1=one, 2=two, 3=three}

}

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4. Custom Routine

Finally, you can write your own routine for this simple task. The idea is to iterate over the map and add each mapping from key K to value V in the specified map.

fun <K, V> clone(original: Map<K, V>): MutableMap<K, V> {

val copy: MutableMap<K, V> = HashMap()

original.forEach { (key, value) -> copy[key] = value }

return copy

}

fun main() {

val map: Map<Int, String> = mutableMapOf(1 to "one", 2 to "two", 3 to "three")

val clone: Map<Int, String> = clone(map)

println(clone) // {1=one, 2=two, 3=three}

}

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That’s all about cloning a map in Kotlin.

1. Using toMap() function

2. Using Copy Constructor

3. Using putAll() function

4. Custom Routine

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1. Using `toMap()` function

3. Using `putAll()` function