Scala数独校验代码报illegal start of statement错误如何解决

报错根本原因 #

你遇到的error: illegal start of statement (no modifiers allowed here)错误是因为：Scala 不允许给函数内部定义的嵌套方法加private访问修饰符，private只能用于类、单例对象的成员属性/方法，函数内部定义的方法天然只在当前函数作用域内可见，不需要也不能加访问修饰符。

其他隐含错误 #

你在validate方法内部定义了BoardParser单例对象，调用它的getValidBoard方法时没有加对象前缀，会报方法不存在的错误。

修复后完整代码 #

def validate(lines: Array[Option[Any]]*): Boolean = {

  object BoardParser {
    /**
     * 从可变参数解析数独棋盘
     * 合法棋盘要求9行9列，非空单元格的值只能是Int或Long类型
     *
     * @param board 可变参数，每个参数是可选值数组
     * @return 代表数独棋盘的二维Int数组，空单元格用0表示
     */
    def getValidBoard(board: Array[Option[Any]]*): Array[Array[Int]] = {
      def validateBoard() = {
        if (board.length != 9 || board.transpose.length != 9) {
          throw new IllegalArgumentException("棋盘必须是9x9的二维数组")
        } else if (!board.forall(isAllNumbers)) {
          throw new IllegalArgumentException("棋盘非空值只能是Int或Long类型")
        }
      }

      validateBoard()
      board.map(toNumbers).toArray
    }

    private def isAllNumbers(line: Array[Option[Any]]) = {
      line.forall {
        case Some(_: Int) => true
        case Some(_: Long) => true
        case None => true
        case _ => false
      }
    }

    private def toNumbers(line: Array[Option[Any]]) = {
      line.map {
        case Some(x: Int) => x
        case Some(x: Long) => x.toInt
        case None => 0
        case _ => throw new IllegalArgumentException
      }
    }
  }

  // 调用BoardParser的方法需要加对象前缀
  val valid_board = BoardParser.getValidBoard(lines)

  def new_validate(board: Array[Array[Int]]): Boolean = {
    lazy val rowsValid = board.forall(hasNoDuplicates)
    lazy val columnsValid = board.transpose.forall(hasNoDuplicates)
    lazy val cellsValid = squaresHaveNoDuplicates(board)

    rowsValid && columnsValid && cellsValid
  }

  // 去掉private修饰符
  def hasNoDuplicates(line: Array[Int]) = line.distinct.count(1 to 9 contains _) == line.count(_ != 0)

  // 去掉private修饰符
  def squaresHaveNoDuplicates(matrix: Array[Array[Int]]) = {
    val rowBlocks = matrix.grouped(3).toArray
    val transposed = rowBlocks.map(_.transpose)
    val squares = transposed.map(_.grouped(3).toArray)
    val squaresFlattened = squares.map(_.map(_.flatten))

    squaresFlattened.forall(_.forall(hasNoDuplicates))
  }

  new_validate(valid_board)
}

改动说明 #

• 移除了嵌套方法hasNoDuplicates、squaresHaveNoDuplicates前面的private修饰符
• 调用getValidBoard时增加了BoardParser.前缀，正确引用内部对象的方法
• 去除了多余的return关键字，Scala 函数最后一行表达式的值默认就是返回值

内容的提问来源于stack exchange，提问作者Shiva ParsaRad