来自“Beginning Scala”的代码示例中的代码错误

发布时间：2020-12-16 19:22:09 所属栏目：安全来源：网络整理

导读：试图在名为“Beginning Scala”的Apress书中运行示例代码.我甚至从他们的网站下载了代码,以确保我没有.获取以下消息： /root/sum.scala:19: error: missing arguments for method collect in trait Iterator;follow this method with `_' if you want to tre

试图在名为“Beginning Scala”的Apress书中运行示例代码.我甚至从他们的网站下载了代码,以确保我没有.获取以下消息：

/root/sum.scala:19: error: missing arguments for method collect in trait Iterator;
follow this method with `_' if you want to treat it as a partially applied function
val lines = input.getLines.collect 
                           ^
one error found

这是我使用的源代码(在Fedora 13上运行Scala版本2.8.1.final(Java HotSpot(TM)Server VM,Java 1.6.0_22)

import scala.io._

def toInt(in: String): Option[Int] =
  try {
    Some(Integer.parseInt(in.trim))
  } catch {
    case e: NumberFormatException => None
  }

def sum(in: Seq[String]) = {
  val ints = in.flatMap(s => toInt(s))
  ints.foldLeft(0)((a,b) => a + b)
}

println("Enter some numbers and press ctrl-D (Unix/Mac) ctrl-C (Windows)")

val input = Source.fromInputStream(System.in)

val lines = input.getLines.collect

println("Sum "+sum(lines))

看起来这是相关的变化：

The Iterator.collect() method in 2.7.7 returns a Seq. In 2.8,it is used to perform a conditional map using a PartialFunction. You can use input.getLines.toSeq instead.

解决方法

啊,我记得这个：

编辑：更深入的答案取代

The code was written against Scala
2.7.3 and 2.8 introduces some breaking changes.

Here’s an update to the code that
works under Scala 2.8.0:

import scala.io._

object Sum {
  def main(args: Array[String]): Unit = {
    println("Enter some numbers and press ctrl-D (Unix/Mac) ctrl-Z (Windows)")
    val input = Source.fromInputStream(System.in)
    val lines = input.getLines.toList
    println("Sum " + sum(lines))
  }

  def toInt(s: String): Option[Int] = {
    try {
      Some(Integer.parseInt(s))
    } catch {
        case e: NumberFormatException => None
    }
  }

  def sum(in: Seq[String]): Int = {
    val ints = in.flatMap(toInt(_))
    ints.foldLeft(0)((a,b) => a + b)
  }

}

资料来源：http://scala-programming-language.1934581.n4.nabble.com/Beginning-Scala-book-problem-td2966867.html

（编辑：李大同）

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