Simple file read with Scala ARM library

Question

I am using the ARM library to read a resource file into a string. The code I'm using is this:

def readResource(reosurceName: String): String = {
  val res = for (writer <- managed(new StringWriter);
                 is     <- managed(this.getClass.getClassLoader.getResourceAsStream(resourceName))) yield {
    IOUtils.copy(is, writer)
    writer.toString
  }
  res.acquireAndGet(identity)
}

It looks a bit weird to me, especially the last part with acquireAndGet of identity. Is there a better way ?

The general question would be, how would you use this style to do something like this

val x: String=
  for (res1 <- managed(...);
       res2 <- managed(...);
       ...
       resn <- managed) yield {
      f(res1, res2, ..., resn)
  }

The behavior is that if the operations within the for comprehension fail I would like the exception to be propagated out of the method and the resources should be closed.

I saw that map on a ManagedResource returns an ExtractableManagedResource from which I can extract the result using the opt method. flatMap returns only a ManagedResource. Is there a reason for this ?

Answer 1

I find it weird too that map and flatMap should behave in a slightly different way.
Maybe the mapping operation gives more freedom to expose a simplified result that can't be obtained through flatMap.

Anyway you could structure the code as follows to get something that looks more appealing

def readResource(resourceName: String): Option[String] = {
  val managedWriter = {
      managed(new StringWriter) and
      managed(this.getClass.getClassLoader.getResourceAsStream(resourceName))
    } map { case (writer, is) => 
        IOUtils.copy(is, writer)
        writer.toString
    }
  }
  managedWriter.opt
}

warn: the code is not tested