Go empty interface value that is actually of type []string to a comma-separated string

interface_slice.go

package main

import (
	"encoding/json"
	"fmt"
	"reflect"
	"strings"
)

type Product struct {
	OutProduct map[string]interface{} `json:"out_product"`
}

func main() {
	raw := []byte(`{"out_product": {"test": ["hello", "hi"]}}`)
	p := Product{}
	_ = json.Unmarshal(raw, &p)
	switch val := p.OutProduct["test"].(type) {
	case interface{}:
		v := reflect.ValueOf(val)
		if v.Kind() != reflect.Slice {
			fmt.Println("not a slice")
			return
		}

		n := make([]string, v.Len())

		for i := 0; i < v.Len(); i++ {
			switch val := v.Index(i).Interface().(type) {
			case string:
				n[i] = val
			default:
				break
			}
		}

		result := strings.Join(n, ", ")
		fmt.Printf("result is: %v", result)

	default:
		fmt.Println("not an interface{}")

	}
}