Workaround for lack of support for array constants?

Go doesn't have array constants.

My application receives messages containing several types of numeric codes which I need to display as phrases.

If array contants existed I could do something like:

<!-- language: go -->

func foo() {
   ...
   fmt.Println(facename[f])
   ...
}
const facename [...]string = "top", "bottom", "left", "right", "front", "back"

But of course there's no way to do this. The first way around this that occurs to me, and maybe a reasonable efficient one is to use a switch

<!-- language: go -->

func foo() {
   ...
   name := "unknown"
   switch f {
   case 0:
      name = "top"
   case 1:
      name = "bottom"
   case 2:
      name = "left"
   case 3:
      name = "right"
   case 4:
      name = "front"
   case 5:
      name = "back"
   }
   fmt.Println(name)
   ...
}

The above is rather tedious if the number of values gets to be twenty or more.

It seems the most concise way is something like

<!-- language: go -->

func foo() {
   ...
   fmt.Println(strings.Split(facenames,",")[f])
   ...
}
const facenames = "top,bottom,left,right,front,back"

I will also have to check that the index is in range of course.
Although efficiency isn't a concern at the moment, it bugs me that
I'm using strings.Split() more than I want to.

Is there another way that is either idiomatic or both concise and efficient?

The idiomatic approach is to use a package level variable:

var facename = []string{"top", "bottom", "left", "right", "front", "back"}

func foo() {
    // ...
    fmt.Println(facename[f])
    // ...
}

It's also idiomatic to use a slice instead of an array in this situation.

It may not be a good fit, but it appears your use case is basically an enum with string equivalents. For this I usually do something along the lines of:

type Face uint8

const (
	FaceTop Face = iota
	FaceBottom
	FaceLeft
	FaceRight
	FaceFront
	FaceBack
)

func (f Face) String() string {
	switch f {
	case FaceTop: return "top"
	case FaceBottom: return "bottom"
	case FaceLeft: return "left"
	case FaceRight: return "right"
	case FaceFront: return "front"
	case FaceBack: return "back"
    default: return ""  // Or add an error return, or add a zero value to the enum
	}
}

func ParseFace(in string) (Face,error) {
	switch in {
	case "top": return FaceTop,nil
	case "bottom": return FaceBottom,nil
	case "left": return FaceLeft,nil
	case "right": return FaceRight,nil
	case "front": return FaceFront,nil
	case "back": return FaceBack,nil
	default: return "",errors.New("invalid face name"+in)
	}
}