1.First of all

I wrote an article in the hope that it will be of benefit to those who are starting Go. When I first saw "..." in the source code, there aren't many information in Japanese even if I googled it, so I will summarize how to use "..." that I often use in business. I thought about it.

1-1. What happens if you read this article

Understand how to use "..." and the points

1-2. Target readers

People who don't understand Go's "..."

2. How to use "..."

2-1. When you want to make the function parameters variable length

Function parameters can be variable length. For example, if you have a function that wants to receive multiple ints in a variable way, you can write: The point is to write ... before the type, like ** ... int **.

//WriteInt is a function that receives and outputs a variable int
func WriteInt(nums ...int) {
	for _, v := range nums {
		fmt.Println(v)
	}
}

When executed, the result is as follows

func main() {
	WriteInt(1, 2, 3)
}

//Execution result
1
2
3

Go Playgroud

2-2. Pass all values to the variadic function

You can pass the variable-length argument function explained in the previous chapter at once by using "...". The point is to write ... after the value you want to pass, such as ** s ... **.

func main() {
	s := []int{1, 2, 3}
	
	//The value that s has...All passed to WriteInt using
	WriteInt(s...)
}

func WriteInt(nums ...int) {
	for _, v := range nums {
		fmt.Println(v)
	}
}

Go Playgroud

It is also useful when appending a slice.

func main() {
	s1 := []int{1, 2, 3}
	s2 := []int{4, 5, 6}
	s3 := append(s1, s2...)
	fmt.Println(s3)
}

//Execution result
[1 2 3 4 5 6]

reference

Official Document Passing_arguments_to ... parameters Official document append 3 dots in 4 places Expand and pass slices to variadic functions with Go ★ Ultimate Guide to Go Variadic Functions

[Go] How to use "... (3 periods)"