Kotlin Set first()
Syntax & Examples

Set.first() extension function

The first() extension function in Kotlin returns the first element in a set. If a predicate is provided, it returns the first element that matches the given predicate.

Syntax of Set.first()

There are 2 variations for the syntax of Set.first() extension function. They are:

1.
fun <T> Set<T>.first(): T

This extension function returns the first element.

Returns value of type T.

2.
fun <T> Set<T>.first(predicate: (T) -> Boolean): T

This extension function returns the first element matching the given predicate.

Returns value of type T.


✐ Examples

1 Getting the first element

Using first() to get the first element in a set.

For example,

  1. Create a set of integers.
  2. Use first() to get the first element in the set.
  3. Print the resulting element.

Kotlin Program

fun main() {
    val numbers = setOf(1, 2, 3, 4, 5)
    val firstNumber = numbers.first()
    println(firstNumber)
}

Output

1

2 Getting the first even number

Using first() to get the first even number in a set.

For example,

  1. Create a set of integers.
  2. Define a predicate function that returns true for even numbers.
  3. Use first() to get the first even number in the set.
  4. Print the resulting number.

Kotlin Program

fun main() {
    val numbers = setOf(1, 3, 5, 6, 7, 8)
    val firstEven = numbers.first { it % 2 == 0 }
    println(firstEven)
}

Output

6

3 Getting the first string with length greater than 2

Using first() to get the first string with a length greater than 2 in a set.

For example,

  1. Create a set of strings.
  2. Define a predicate function that returns true for strings with a length greater than 2.
  3. Use first() to get the first string with a length greater than 2 in the set.
  4. Print the resulting string.

Kotlin Program

fun main() {
    val strings = setOf("a", "ab", "abc", "abcd")
    val firstLongString = strings.first { it.length > 2 }
    println(firstLongString)
}

Output

"abc"

Summary

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