How to Optional Parameters in Go

1. Use the variadic Function to Pass Optional Parameters in Go
2. Use the variadic Function to Pass Multiple Strings in Go

The variadic functions have a variable number of arguments when invoked. It can be used with zero or more arguments.

An ellipsis ... can define a variable function before a parameter.

Use the variadic Function to Pass Optional Parameters in Go

The function will accept any number of ints as inputs. If you already have many args in a slice, use func(slice...) to apply them to a variadic function.

package main

import "fmt"

func sum(nums ...int) {
	fmt.Print(nums, " ")
	total := 0
	for _, num := range nums {
		total += num
	}
	fmt.Println(total)
}
func main() {
	sum(1, 2)
	sum(1, 2, 3)
	nums := []int{1, 2, 3, 4}
	sum(nums...)
}

Output:

[1 2] 3
[1 2 3] 6
[1 2 3 4] 10

Use the variadic Function to Pass Multiple Strings in Go

The number of parameters supplied to the s parameter has no restriction. The tree-dotted ellipsis informs the compiler that this string can have any number of values from zero to many.

package main

import "fmt"

func main() {
	variadic()
	variadic("white", "black")
	variadic("white", "black", "blue")
	variadic("white", "black", "blue", "purple")
}
func variadic(s ...string) {
	fmt.Println(s)
}

Output:

[]
[white black]
[white black blue]
[white black blue purple]

Let’s make a program that says hello to folks when their names are supplied to the function:

package main

import "fmt"

func main() {
	sayHello()
	sayHello("Jay")
	sayHello("Jessica", "Mark", "Jonas")
}

func sayHello(names ...string) {
	for _, n := range names {
		fmt.Printf("Hello %s\n", n)
	}
}

Output:

Hello Jay
Hello Jessica
Hello Mark
Hello Jonas