closing file pointer in Scala in Finally - scala

Question

In the following code, I am reading no. of lines from a file. If something goes wrong, I'll like to close the file pointer. But how can I find out if f contains valid pointer or not?
def countLines(filename:String):Option[Int] = {
try{
val f = Source.fromFile(filename)
println(s"no. of lines ${f.getLines().size}")
Some(f.getLines.size)
} catch {
case ex: FileNotFoundException => {
println(s"file ${filename} not found")
None
}
} finally {
//f might not be a valid pointer depending on when the error occured
}
}
The book I am reading uses var to maintain state (if f is valid or not) but I am trying to avoid it for sake of using only immutable variables.
def countLines(filename:String):Option[Int] = {
var f:Option[Source] = None
try{
f = Some(Source.fromFile(filename))
println(s"no. of lines ${f.get.getLines().size}")
Some(f.get.getLines.size)
} catch {
case ex: FileNotFoundException => {
println(s"file ${filename} not found")
None
}
} finally {
for(i<-f){
println("closing file")
i.close()
}
}
}

Answer 1

A double Try(). This closes the io resource even if the getLines() fails, but only if the fromFile() succeeds.
import scala.util.Try
def countLines(filename: String): Option[Int] =
Try(io.Source.fromFile(filename)).fold(_ => None, {f =>
val count = Try(f.getLines().length)
f.close()
count.toOption
})

Answer 2

What do you think about this?
If you want Scala-way - i think it's good example for your task:
def countLines(filename: String): Try[Int] = Try(Source.fromFile(filename).getLines.toList.size)
def test() = {
val filename = "/etc/passwd"
countLines(filename) match {
case Success(n) => println(n)
case Failure(f) => println(f)
}
}
When n - is a number of our lines, and f - is a Throwable.

Answer 3

How about this:
def countLines(filename: String): Option[Int] = {
val file = Try(Source.fromFile(filename))
val count = file.map(_.getLines().size)
(for {
_ <- count.recoverWith { case _ => file.map(_.close()) }
lineCount <- count
} yield lineCount).toOption
}
Let's analyze it:
If file does not exist we will have failed Try instance and method returns None. In this case you do not need to clear any resources as no actual stream was created.
If getLines fails for any reason or anything else during processing goes south we will close created stream in first line of for comprehension
Hope it helps

Answer 4

Simply, how about this:
def numLines(fileName:String):Option[Int] = {
try {
val f = scala.io.Source.fromFile(fileName)
try { Some(f.getLines.size) }
catch { case ex: IOException =>
Console.err.println("i/o excetion")
None
}
finally { f.close() }
}
catch {
case ex: FileNotFoundException =>
Console.err.println("file not found")
None
}
}