Scala和案例类(Scala and case classes)

 我正在阅读文件，并将行号附加到每个文件。 下面是一个列表来帮助这个例子： 
 
 val testList: List[String] = List("Dont", "Do", "It" ） 
 
val output: List[(String, Int)] = (testList.zipWithIndex)
 
 我的程序使用._1＆._2访问器获得了一点代码嗅觉。 我创建： 
 
case class File(line: String, lineNum: Int)
 
 但是，我知道如何最好地利用这个案例类的唯一方法是使用以下内容： 
 
val fileOutput: List[File] = for{(line, lineNum) <- output} yield{File(line, lineNum)}
 
 我的问题：为什么我不能这样做？ 
 
val output: List[File] = (testList.zipWithIndex)
 
 为了使用案例课程，我对我的文件做了两个通行证感到厌倦。 
 
 提前致谢 

I am reading in a file, and appending line numbers to each file. Below is a List to facilitate this example:
 
val testList: List[String] = List("Dont", "Do", "It") 
 
val output: List[(String, Int)] = (testList.zipWithIndex)
 
My program is getting a bit of code-smell with using the ._1 & ._2 accessors. I created:
 
case class File(line: String, lineNum: Int)
 
However, the only way I know how to make best use of this case class would be to use the following:
 
val fileOutput: List[File] = for{(line, lineNum) <- output} yield{File(line, lineNum)}
 
My question: why can't I do this? 
 
val output: List[File] = (testList.zipWithIndex)
 
I'm a bit weary of doing two passes on my file for the sake of using a case-class.
 
Thanks in advance

原文：https://stackoverflow.com/questions/40393617