Go ellipses
last modified April 11, 2024
In this article we show how to use the ellipses operator.
The ellipses (...) (or three dots) operator is used in variadic functions, array literals and go commands.
$ go version go version go1.22.2 linux/amd64
We use Go version 1.22.2.
Go variadic function parameters
Variadic functions can be called with any number of trailing arguments.
package main
import "fmt"
func main() {
fmt.Println(Sum(1, 2, 3))
fmt.Println(Sum(1, 2, 3, 4))
fmt.Println(Sum(1, 2, 3, 4, 5))
}
func Sum(n ...int) int {
sum := 0
for _, n := range n {
sum += n
}
return sum
}
In the example, we have the Sum function which can accept any
number of integer values.
$ go run main.go 6 10 15
We can use the three dots when we pass a slice as the argument to the variadic function.
package main
import "fmt"
func main() {
vals := []int{1, 2, 3, 4, 5, 6, 7}
fmt.Println(Sum(vals...))
}
func Sum(n ...int) int {
sum := 0
for _, n := range n {
sum += n
}
return sum
}
In the example we pass a slice of integers to the Sum function.
Infering array length
We can infer the array length when using array literals with the ellipses
... operator.
package main
import "fmt"
func main() {
vals := [...]int{ 1, 2, 3, 4, 5, 6 }
fmt.Println(vals)
}
In the code example, we use the ... in the array declaration. This
tells Go to infer the length of the array from the provided array literal.
$ go run main.go [1 2 3 4 5 6]
Wildcards
The ellipses can be used as wildcars in go commands.
$ go list ... archive/tar archive/zip bufio bytes compress/bzip2 compress/flate compress/gzip compress/lzw compress/zlib container/heap container/list container/ring context crypto crypto/aes crypto/cipher ...
The command lists all packages recursively, including the packages from the standard library in the current directory.
Source
The Go Programming Language Specification
In this article we have covered the ellipses (three dots) operator in Golang.
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