How to Use vararg in Kotlin: Syntax and Examples

In Kotlin, use vararg before a parameter type to allow passing a variable number of arguments to a function. This lets you call the function with zero or more values, which Kotlin treats as an array inside the function.

Syntax

The vararg keyword is placed before the parameter name in a function declaration to accept multiple arguments as an array.

• vararg paramName: Type — declares a variable number of arguments of the specified type.
• Inside the function, the paramName behaves like an array of Type.
• You can pass zero or more arguments when calling the function.

kotlin

fun printAll(vararg messages: String) {
    for (m in messages) println(m)
}

Example

This example shows a function using vararg to print any number of strings passed to it.

kotlin

fun printAll(vararg messages: String) {
    for (m in messages) println(m)
}

fun main() {
    printAll("Hello", "World", "from", "vararg")
    printAll("Single argument")
    printAll() // no arguments
}

Output

Hello
World
from
vararg
Single argument

Common Pitfalls

Common mistakes when using vararg include:

• Trying to declare more than one vararg parameter in a function (only one is allowed).
• Passing an array directly without using the spread operator *.
• Confusing vararg with regular array parameters.

Use the spread operator * to pass an existing array to a vararg parameter.

kotlin

fun printAll(vararg messages: String) {
    for (m in messages) println(m)
}

fun main() {
    val array = arrayOf("A", "B", "C")
    // Wrong: printAll(array) // Error: type mismatch
    printAll(*array) // Correct: spread operator used
}

Output

A
B
C

Quick Reference

Concept	Description
vararg parameter	Allows passing variable number of arguments as an array
Only one vararg	A function can have only one vararg parameter
Spread operator (*)	Used to pass an existing array to a vararg parameter
Inside function	Vararg parameter behaves like an array
Zero arguments	You can call the function with no arguments

Key Takeaways

Use vararg to accept a flexible number of arguments in Kotlin functions.

Only one vararg parameter is allowed per function.

Use the spread operator * to pass an array to a vararg parameter.

Inside the function, the vararg parameter acts like an array.

You can call a vararg function with zero or more arguments.