Scala 示例代码和弃用问题

Question

我正在阅读 Programming Scala (O'reilly)这是一本非常好的书，而且很容易理解。

问题是有一个关于枚举的例子被窃听了，作为一个初学者真的不知道为什么会这样。

所以，这是代码:

// code-examples/Rounding/enumeration-script.scala

object Breed extends Enumeration {
  val doberman = Value("Doberman Pinscher")
  val yorkie = Value("Yorkshire Terrier")
  val scottie = Value("Scottish Terrier")
  val dane = Value("Great Dane")
  val portie = Value("Portuguese Water Dog")
}

// print a list of breeds and their IDs
println("ID\tBreed")
for (breed <- Breed) println(breed.id + "\t" + breed)

// print a list of Terrier breeds
println("\nJust Terriers:")
Breed.filter(_.toString.endsWith("Terrier")).foreach(println)

当我尝试在 eclipse 中执行它时(在 main 方法内部)，它甚至无法编译。当我想用 scala 命令执行脚本时，它可以工作，但说有弃用警告。所以我用 -deprecation 标志再次执行它并显示警告:

>> scala -deprecation enumeration-script.scala
/home/{me}/code/enumeration-script.scala:13: warning: method foreach in class Enumeration is deprecated: use values.foreach instead
for (breed <- Breed) println(breed.id + "\t" + breed)
              ^
/home/{me}/code/enumeration-script.scala:17: warning: method filter in class Enumeration is deprecated: use values.filter instead
Breed.filter(_.toString.endsWith("Terrier")).foreach(println)
      ^
two warnings found
ID  Breed
0   Doberman Pinscher
1   Yorkshire Terrier
2   Scottish Terrier
3   Great Dane
4   Portuguese Water Dog

Just Terriers:
Yorkshire Terrier
Scottish Terrier

所以，我读了这篇文章并更改了代码，现在它工作正常，更改是:

// code-examples/Rounding/enumeration-script.scala

object Breed extends Enumeration {
  val doberman = Value("Doberman Pinscher")
  val yorkie = Value("Yorkshire Terrier")
  val scottie = Value("Scottish Terrier")
  val dane = Value("Great Dane")
  val portie = Value("Portuguese Water Dog")
  def main(args: Array[String]) {
    // print a list of breeds and their IDs
    println("ID\tBreed")
    for (breed <- Breed.values) println(breed.id + "\t" + breed)

    // print a list of Terrier breeds
    println("\nJust Terriers:")
    Breed.values.filter(_.toString.endsWith("Terrier")).foreach(println)
  }
}

请注意，我将执行代码放在 main 方法中。

现在，这是为什么呢？是针对Scala的版本？我应该担心其他例子吗？更新我的 Scala 版本？为什么它不在 eclipse 上运行？

我的 Scala 版本是 2.8.1.final

Answer 1

所以，我在书的勘误表中找到了它:

Under version 2.8.0.Beta1-prerelease, there are deprecation warnings with the source code.

作者回复:

Yes, apparently this is an API change in 2.8. If you run the script with "scala -deprecation ...", you'll see the warnings in more detail (I wish this flag was on by default). You have to use "for (breed <- Breed.values)" instead of "for (breed <- Breed)" and similarly, "Breed.values.filter" instead of "Breed.filter" to eliminate the warnings. However, the values method isn't available in 2.7.X.