Go Unpacking Array As Arguments

Question

So in Python and Ruby there is the splat operator (*) for unpacking an array as arguments. In Javascript there is the .apply() function. Is there a way of unpacking an array/slice as function arguments in Go? Any resources for this would be great as well!

Something along the lines of this:

func my_func(a, b int) (int) {
    return a + b
}

func main() {
    arr := []int{2,4}
    sum := my_func(arr)
}

I do apologize if I'm making an syntactical/assorted mistakes. I'm new to Go.

Answer 1

You can use a vararg syntax similar to C:

package main
import "fmt"

func my_func( args ...int) int {
   sum := 0
   for _,v := range args {
      sum = sum + v
   }

   return sum;
}

func main() {
    arr := []int{2,4}
    sum := my_func(arr...)
    fmt.Println("Sum is ", sum)
}

Now you can sum as many things as you'd like. Notice the important ... after when you call the my_func function.

Running example: http://ideone.com/8htWfx

Answer 2

Either your function is varargs, in which you can use a slice with the ... notation as Hunter McMillen shows, or your function has a fixed number of arguments and you can unpack them when writing your code.

If you really want to do this dynamically on a function of fixed number of arguments, you can use reflection:

package main
import "fmt"
import "reflect"

func my_func(a, b int) (int) {
    return a + b
}

func main() {
    arr := []int{2,4}
    var args []reflect.Value
    for _, x := range arr {
        args = append(args, reflect.ValueOf(x))
    }
    fun := reflect.ValueOf(my_func)
    result := fun.Call(args)
    sum := result[0].Interface().(int)
    fmt.Println("Sum is ", sum)
}

Answer 3

https://play.golang.org/p/2nN6kjHXIsd

I had a reason to unpack some vars from a map[string]string with single quotes around some of them as well as without. Here's the logic for it and the play link up top has the full working snippet.

func unpack(a map[string]string) string {

var stmt, val string
var x, y []string
for k, v := range a {
    x = append(x, k)
    y = append(y, "'"+v+"'")
}

stmt = "INSERT INTO tdo.rca_trans_status (" + strings.Join(x, ", ")
val = ") VALUES (" + strings.Join(y, ",") + ");"

return stmt + val}

Which presents cleanly for a mssql query as:

INSERT INTO tdo.rca_trans_status (rca_json_body, original_org, md5sum, updated, rca_key) VALUES ('blob','EG','2343453463','2009-11-10 23:00:00','prb-180');

Answer 4

No, there's no direct support for this in the language. Python and Ruby, as well as Javascript you're mentioning; are all dynamic/scripting languages. Go is way closer to, for example, C than to any dynamic language. The 'apply' functionality is handy for dynamic languages, but of little use for static languages like C or Go,