功能性尝试&赶上斯卡拉 [英] functional try & catch w/ Scala

问题描述

在Scala中打开一个资源并应用其方法比使用 vals 这个方法（直接从java中直接转换）还有一种更具象征意义的方式，等等。

Is there a more idomatic way of opening a resource in Scala and applying methods to it than this method (tranlsated directly from java), using vals but also including the finally etc.

var is:FileInputStream = null
try {
  is = new FileInputStream(in)
  func(is)
} catch {
  case e:IOException =>
    println("Error: could not open file.")
    println("       -> " + e)
    exit(1)
} finally {
  if(is) is.close()
}

推荐答案

在Github的Josh Suereth的 scala-arm 库中以各种方式实施贷款模式。

The loan pattern is implemented in various ways in Josh Suereth's scala-arm library on github.

然后您可以使用这样的资源：

You can then use a resource like this:

val result = managed(new FileInputStream(in)).map(func(_)).opt 

，它将返回包装在 Option 中的 func 的结果，并负责关闭输入流。

which would return the result of func wrapped in an Option and take care of closing the input stream.

要处理创建资源时可能出现的异常，可以将它与 scala.util.control结合使用。 Exception object：

To deal with the possible exceptions when creating the resource, you can combine with the scala.util.control.Exception object:

import resource._
import util.control.Exception.allCatch

allCatch either { 
  managed(new FileInputStream(in)).map(func(_)).opt 
} match {
  case Left(exception) => println(exception)
  case Right(Some(result)) => println(result)
  case _ =>
}

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