Functional try & catch with Scala

Question

Is there a more idiomatic way of opening a resource in Scala and applying methods to it than this method (translated directly from java):

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() } 

Answer 1

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

You can then use a resource like this:

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

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

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 _ => } 

Answer 2

Use the Loan pattern (dead link) non permanent link to new location.