02-Apr-2025

Variadic functions in Go provide a flexible way to work with a variable number of arguments. Similar to the concept of “rest parameters” in JavaScript, Go’s variadic functions allow you to pass zero or more arguments of a specific type to a function.

Declaration

A variadic function is declared using an ellipsis (...) preceding the type name of the variadic parameter. This parameter effectively becomes a slice within the function’s scope.

package main

import "fmt"

func printStrings(strs ...string) {
    for _, str := range strs {
        fmt.Println(str)
    }
}

func main() {
    printStrings("hello", "world", "go")
    printStrings() // Calling with no arguments is also valid
}

Usage

The strs parameter inside printStrings is treated as a slice of strings. You can iterate over it, check its length, or access individual elements just like any other slice.

Passing Slices to Variadic Functions

You can pass an existing slice to a variadic function by appending the ellipsis to the slice variable during the function call. This effectively “unpacks” the slice into individual arguments.

package main

import "fmt"

func sumNumbers(nums ...int) int {
    total := 0
    for _, num := range nums {
        total += num
    }
    return total
}

func main() {
    numbers := []int{1, 2, 3, 4, 5}
    sum := sumNumbers(numbers...) // Unpack the slice
    fmt.Println("Sum:", sum) // Output: Sum: 15


	moreNumbers := []int{10,11}
	combinedSlice := append(numbers, moreNumbers...) // append moreNumbers to numbers
	sum2 := sumNumbers(combinedSlice...) // Unpack the combined slice
	fmt.Println(sum2) // Output: 66
}

Combining with Regular Parameters

Variadic parameters can be combined with regular parameters, but the variadic parameter must always be the last parameter in the function signature.

package main

import "fmt"

func printFormatted(prefix string, values ...interface{}) {
    for _, value := range values {
        fmt.Println(prefix, value)
    }
}

func main() {
    printFormatted("Value:", 1, "hello", 3.14)
}

In this example, prefix is a regular string parameter, and values is a variadic parameter of type interface{}, which allows values of any type to be passed.

Variadic functions provide a concise and elegant way to handle functions that need to accept a variable number of arguments, making your Go code more flexible and readable.