Variadic Functions in Go

A variadic function is a function that can take any number of arguments. A common use case for this is a function that can print out multiple things at once, and in fact Go’s fmt.Println() function is a good example of this. It’s function signature is:

fmt.Println(a ...interface{})

The ...{interface} piece here denotes that Println can take any number of arguments of type empty interface (i.e. anything). So this would work just fine:

func main() {
name := "Eric"
age := 36
 
fmt.Println("Hello,", name, "you are", age, "years old")
}

Passing a Slice to a Variadic Function

If we want to pass a slice to a variadic function — i.e. if we want the function to accept each element of the slice as an input argument — we need to unpack it (I’m not sure if “unpack” is real Go terminology, but it’s the language I’m familiar with). We unpack it by adding a trailing ...

So, for example:

func sum(nums ...int) int {
	total := 0
 
	for _, num := range nums {
		total += num
	}
}
 
func main() {
	x = []int{1, 2, 3}
 
	s := sum(x...) //we add ... after x to unpack it
}

A common use case for this is appending a slice to another slice. We would need to unpack the second slice, e.g.:

x := []int{1, 2, 3}
y := []int{4, 5, 6}
 
//appends y to x
x = append(x, y...)