Variadic Functions

Declaring a Variadic Function

Prefixing the last parameter's type with '...' lets the caller pass any number of arguments of that type, including none at all -- inside the function, that parameter is just a regular slice.

Example: Declaring a Variadic Function

package main

import "fmt"

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

func main() {
	fmt.Println(sum(1, 2, 3, 4))
	fmt.Println(sum())
}

Spreading a Slice into Variadic Arguments

If you already have a slice and want to pass its elements as individual variadic arguments, append '...' after the slice at the call site instead of passing the slice as one value.

Example: Spreading a Slice into Variadic Arguments

package main

import "fmt"

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

func main() {
	values := []int{10, 20, 30}
	fmt.Println(sum(values...))
}

Mixing Regular and Variadic Parameters

A variadic parameter can be combined with regular parameters before it, as long as it remains the final parameter in the list -- a common pattern for functions like a formatted logger that always takes a prefix plus a variable number of values.

Note: Variadic parameters must always come last in the signature.

Example: Mixing Regular and Variadic Parameters

package main

import "fmt"

func logAll(prefix string, values ...int) {
	for _, v := range values {
		fmt.Println(prefix, v)
	}
}

func main() {
	logAll("value:", 1, 2, 3)
}