code: func IndexInSlice(array interface{}, o interface{}, equals Equals) int {
  	arr := reflect.ValueOf(array)
  	for i := 0; i < arr.Len(); i++ {
  		if equals(arr.Index(i).Interface(), o) {
  			return i
  		}
  	}
  	return -1
  }
docs: // IndexInSlice returns the index of given object o in array