受检者与模式类型不兼容；发现：package.SomeObject 需要：单位

Question

我正在尝试使用 scala 中的文件搜索器程序。

FileChecker.scala

package fileSearcher

import sun.org.mozilla.javascript.internal.ast.Yield

class FilterChecker(filter:String) {

def matches(content: String) = content contains filter

def findMatchedFiles(fileObjects: List[IOObject]) =

  for(fileObject <- fileObjects
      if(fileObject.isInstanceOf[FileObject])
      if(matches(fileObject.name)))
    yield fileObject

}

object FilterChecker{

  def apply(filter: String)=new FilterChecker(filter)
}

IOObject.scala

package fileSearcher
import java.io.File
trait IOObject {
  val file:File
  val name= file.getName()
}

case class FileObject(file: File)extends IOObject
case class DirectoryObject(file: File)extends IOObject

FileConverter.scala

package fileSearcher

import java.io.File

object FileConverter {
def convertToIOObject(file: File){
  if(file.isDirectory()) DirectoryObject(file)
  else FileObject(file)
}
}

Matcher.scala

package fileSearcher

import java.io.File

class Matcher(filter:String,rootLocation:String) {
val rootIOObject=FileConverter.convertToIOObject(new File(rootLocation))

def execute()={
  val matchedFiles= rootIOObject  match {
    case file : FileObject if FilterChecker(filter) matches file.name =>List(file)  //error 1
    case directory: DirectoryObject => ???    //error 2
    case _ => List()

  }
  matchedFiles map(iOObject => iOObject.name) 
 }
}

上面的代码给出了 2 个错误。

scrutinee is incompatible with pattern type; found : fileSearcher.FileObject required: Unit
scrutinee is incompatible with pattern type; found : fileSearcher.DirectoryObject required: Unit

谁能解释一下我做错了什么，我该如何解决？

谢谢

Answer 1

您缺少一个等号：

def convertToIOObject(file: File) = {
                                  ^
                                  here

没有它，编译器假定方法 returns Unit，这就是 match 语句被混淆的原因：它不能是 FileObject 或DirectoryObject 如果必须是 Unit.

受检者与模式类型不兼容；发现：package.SomeObject 需要：单位

scrutinee is incompatible with pattern type; found : package.SomeObject required: Unit

scala

pattern-matching

sbt

case