Kotlin List withIndex()
Syntax & Examples

Syntax of List.withIndex()

The syntax of List.withIndex() extension function is:

fun <T> Iterable<T>.withIndex(): Iterable<IndexedValue<T>>

This withIndex() extension function of List returns a lazy Iterable that wraps each element of the original collection into an IndexedValue containing the index of that element and the element itself.


✐ Examples

1 Example

In this example,

  • We create a list named list containing the characters 'a', 'p', 'p', 'l', 'e'.
  • We use the withIndex() extension function on list to create an iterable of indexed values.
  • We iterate over the indexed list using a loop and print each index-value pair to standard output.

Kotlin Program

fun main(args: Array<String>) {
    val list = listOf(&quot;a&quot;, &quot;p&quot;, &quot;p&quot;, &quot;l&quot;, &quot;e&quot;)
    val indexedList = list.withIndex()
    for ((index, value) in indexedList) {
        println(&quot;Index: \$index, Value: \$value&quot;)
    }
}

Output

Index: 0, Value: a
Index: 1, Value: p
Index: 2, Value: p
Index: 3, Value: l
Index: 4, Value: e

2 Example

In this example,

  • We create a list named list containing the integers 10, 20, 30.
  • We use the withIndex() extension function on list to create an iterable of indexed values.
  • We iterate over the indexed list using a loop and print each index-value pair to standard output.

Kotlin Program

fun main(args: Array<String>) {
    val list = listOf(10, 20, 30)
    val indexedList = list.withIndex()
    for ((index, value) in indexedList) {
        println(&quot;Index: \$index, Value: \$value&quot;)
    }
}

Output

Index: 0, Value: 10
Index: 1, Value: 20
Index: 2, Value: 30

3 Example

In this example,

  • We create a list named list containing the strings 'apple', 'banana', 'cherry'.
  • We use the withIndex() extension function on list to create an iterable of indexed values.
  • We iterate over the indexed list using a loop and print each index-value pair to standard output.

Kotlin Program

fun main(args: Array<String>) {
    val list = listOf(&quot;apple&quot;, &quot;banana&quot;, &quot;cherry&quot;)
    val indexedList = list.withIndex()
    for ((index, value) in indexedList) {
        println(&quot;Index: \$index, Value: \$value&quot;)
    }
}

Output

Index: 0, Value: apple
Index: 1, Value: banana
Index: 2, Value: cherry

Summary

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