KotlinVararg Parameters in Functions

Syntax

  • Vararg Keyword: vararg is used in a method declaration to indicate that a variable number of parameters will be accepted.
  • Spread Operator: An asterisk (*) before an array that is used in function calls to "unfold" the contents into individual parameters.

Basics: Using the vararg keyword

Define the function using the vararg keyword.

fun printNumbers(vararg numbers: Int) {
    for (number in numbers) {
        println(number)
    }
}

Now you can pass as many parameters (of the correct type) into the function as you want.

printNumbers(0, 1)                // Prints "0" "1"
printNumbers(10, 20, 30, 500)     // Prints "10" "20" "30" "500"

Notes: Vararg parameters must be the last parameter in the parameter list.

Spread Operator: Passing arrays into vararg functions

Arrays can be passed into vararg functions using the Spread Operator, *.

Assuming the following function exists...

fun printNumbers(vararg numbers: Int) {
    for (number in numbers) {
        println(number)
    }
}

You can pass an array into the function like so...

val numbers = intArrayOf(1, 2, 3)
printNumbers(*numbers)

// This is the same as passing in (1, 2, 3)

The spread operator can also be used in the middle of the parameters...

val numbers = intArrayOf(1, 2, 3)
printNumbers(10, 20, *numbers, 30, 40)

// This is the same as passing in (10, 20, 1, 2, 3, 30, 40)