Kotlin Tutorials

Kotlin Set toMutableSet()
Syntax & Examples

toMutableSet() extension function

The toMutableSet() extension function in Kotlin returns a new MutableSet containing all distinct elements from the given collection.

Syntax of toMutableSet()

The syntax of Set.toMutableSet() extension function is:

fun <T> Iterable<T>.toMutableSet(): MutableSet<T>

This toMutableSet() extension function of Set returns a new MutableSet containing all distinct elements from the given collection.

Return Type

Set.toMutableSet() returns value of type MutableSet.


✐ Examples

1 Converting a set of integers to a MutableSet

Using toMutableSet() to convert a set of integers to a MutableSet.

For example,

  1. Create a set of integers.
  2. Use toMutableSet() to convert the set to a MutableSet.
  3. Print the resulting MutableSet.

Kotlin Program

fun main() {
    val intSet = setOf(1, 2, 3, 4, 5)
    val mutableSet = intSet.toMutableSet()
    println(mutableSet)
}

Output

[1, 2, 3, 4, 5]

2 Converting a set of strings to a MutableSet

Using toMutableSet() to convert a set of strings to a MutableSet.

For example,

  1. Create a set of strings.
  2. Use toMutableSet() to convert the set to a MutableSet.
  3. Print the resulting MutableSet.

Kotlin Program

fun main() {
    val stringSet = setOf("one", "two", "three")
    val mutableSet = stringSet.toMutableSet()
    println(mutableSet)
}

Output

[one, two, three]

3 Converting a set of custom objects to a MutableSet

Using toMutableSet() to convert a set of custom objects to a MutableSet.

For example,

  1. Create a data class.
  2. Create a set of custom objects.
  3. Use toMutableSet() to convert the set to a MutableSet.
  4. Print the resulting MutableSet.

Kotlin Program

data class Person(val name: String, val age: Int)

fun main() {
    val peopleSet = setOf(Person("Alice", 30), Person("Bob", 25), Person("Charlie", 35))
    val mutableSet = peopleSet.toMutableSet()
    println(mutableSet)
}

Output

[Person(name=Alice, age=30), Person(name=Bob, age=25), Person(name=Charlie, age=35)]

Summary

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