Question

以下使用scopt：

import java.io.File

object Application extends App {

  case class Config(in: File = new File("."), out: File = new File("."), scripts: Seq[File] = Seq())

  val parser = new scopt.OptionParser[Config]("scopt") {
    head("Script Runner", "0.1")
    opt[File]('i', "in") required () valueName ("<path>") action { (x, c) =>
      c.copy(in = x)
    } text ("required in path property")
    opt[File]('o', "out") required () valueName ("<path>") action { (x, c) =>
      c.copy(out = x)
    } text ("required out path file property")
    arg[File]("<file>...") unbounded () required() action { (x, c) =>
      c.copy(scripts = c.scripts :+ x)
    } text ("unbounded script paths")
  }

  val config = parser.parse(args, Config())

  val scripts = config.map { argConfig => argConfig.scripts }

  config match {
    case Some(config) => println(config)
    case _ => println("config undefined")
  }
}

我收到编译错误：

[error] /Users/jamesclark/code/scratch/src/main/scala/Application.scala:13: not found: value x
[error]       c.copy(out = x)

如果我重命名Config参数scripts或val scripts，则会进行编译。

任何人都可以告诉我这里发生了什么？这是一个编译器问题，还是我错过了一些魔术？

scala 2.11.8 / sbt 0.13.7 / scopt 3.5.0

Answer 1

将parser，config和scripts纳入lazy val而不是val s会产生更有用的错误消息：/src/main/scala/Application.scala:23: variable definition needs type because 'scripts' is used as a named argument in its body.

为脚本提供类型注释val scripts: Option[Seq[File]] = ...可以解决问题。

解决此问题的其他方法是重命名val scripts或case class Config(... scripts: Seq[File] ...) scripts次出现。

问题的根源似乎来自scopt库，因为将parser的定义移动到单独的范围不需要任何重命名或类型注释工作。

object Application extends App {

  def newParser(): OptionParser[Config] = {
    new scopt.OptionParser[Config]("scopt") {
      head("Script Runner", "0.1")

      opt[File]('i', "in") required () valueName ("<path>") action { (x, c) =>
        c.copy(in = x)
      } text ("required in path property")

      opt[File]('o', "out") required () valueName ("<path>") action { (x, c) =>
        c.copy(out = x)
      } text ("required out path file property")

      arg[File]("<file>...") unbounded () required() action { (x, c) =>
        c.copy(scripts = c.scripts :+ x)
      } text ("unbounded script paths")
    }
  }

  case class Config(in: File = new File("."), out: File = new File("."), scripts: Seq[File] = Seq())

  val parser = newParser()

  val config = parser.parse(args, Config())

  val scripts = config.map { argConfig => argConfig.scripts }

  config match {
    case Some(config) =>
      println(config)
    case _ =>
      println("config undefined")
  }
}

scopt＆＃34;未找到：价值＆＃34;定义具有相同名称的val

1 个答案: