   }()
 
   // "I give %d apples to %@" --> [.Int, .String]
-  private static func placeholders(fromFormat formatString: String) -> [PlaceholderType] {
+  private static func placeholders(fromFormat formatString: String) throws -> [PlaceholderType] {
     let range = NSRange(location: 0, length: (formatString as NSString).length)
 
     // Extract the list of chars (conversion specifiers) and their optional positional specifier

      }
    }

    public static func placeholders(fromFormat str: String) -> [PlaceholderType] {
      return StringsFileParser.placeholders(fromFormat:  str)
    }
  }


          while list.count <= insertionPos-1 {
            list.append(.unknown)
          }
          let previous = list[insertionPos-1]
          guard previous == .unknown || previous == p else {
            throw StringsFileParserError.invalidPlaceholder(previous: previous, new: p)
          }
          list[insertionPos-1] = p
        }
      }
