How to use Using (with Source.fromFile) and handle error - scala

Question

This is a follow up question to https://stackoverflow.com/a/55440851/2691976
I have the following code
import scala.io.Source
import scala.util.Using
object Problem {
def main(args: Array[String]): Unit = {
Using(Source.fromFile("thisfileexists.txt")) { source =>
println(1 / 1)
println(1 / 0)
}
}
}
Running it with scala3, it will just print out 1 single line and no error.
scala3 test.scala
1
I am expecting an error like the following,
Exception in thread "main" java.lang.ArithmeticException: / by zero
at Problem$.main(test.scala:10)
at Problem.main(test.scala)
at sun.reflect.NativeMethodAccessorImpl.invoke0(Native Method)
at sun.reflect.NativeMethodAccessorImpl.invoke(NativeMethodAccessorImpl.java:62)
at sun.reflect.DelegatingMethodAccessorImpl.invoke(DelegatingMethodAccessorImpl.java:43)
at java.lang.reflect.Method.invoke(Method.java:498)
at dotty.tools.scripting.ScriptingDriver.compileAndRun(ScriptingDriver.scala:42)
at dotty.tools.scripting.Main$.main(Main.scala:43)
at dotty.tools.MainGenericRunner$.run$1(MainGenericRunner.scala:230)
at dotty.tools.MainGenericRunner$.main(MainGenericRunner.scala:239)
at dotty.tools.MainGenericRunner.main(MainGenericRunner.scala)
at sun.reflect.NativeMethodAccessorImpl.invoke0(Native Method)
at sun.reflect.NativeMethodAccessorImpl.invoke(NativeMethodAccessorImpl.java:62)
at sun.reflect.DelegatingMethodAccessorImpl.invoke(DelegatingMethodAccessorImpl.java:43)
at java.lang.reflect.Method.invoke(Method.java:498)
at coursier.bootstrap.launcher.a.a(Unknown Source)
at coursier.bootstrap.launcher.Launcher.main(Unknown Source)
So why does it not print out error when I am using Using (which I suspect it is causing the problem here)?
And what is the solution so I can use both Using and Source.fromFile with potential error?
I have read the Using Scala 2 doc and Scala 3 doc but it doesn't say anything about error
In case this is important, I am using Mac
scala3 --version
Scala code runner version 3.1.2-RC1-bin-20211213-8e1054e-NIGHTLY-git-8e1054e -- Copyright 2002-2021, LAMP/EPFL

Answer 1

Thats because Using returns Try as you can see here
https://www.scala-lang.org/api/2.13.x/scala/util/Using$.html#apply[R,A](resource:=%3ER)(f:R=%3EA)(implicitevidence$1:scala.util.Using.Releasable[R]):scala.util.Try[A]
You can use .fold, .get, pattern matching, etc.
for example:
import scala.io.Source
import scala.util.Using
object Problem {
def main(args: Array[String]): Unit = {
Using(Source.fromFile("thisfileexists.txt")) { source =>
println(1 / 1)
println(1 / 0)
}.get
}
}
or as follows:
import scala.io.Source
import scala.util.Using
import scala.util._
object Problem {
def main(args: Array[String]): Unit = {
Using(Source.fromFile("thisfileexists.txt")) { source =>
println(1 / 1)
println(1 / 0)
} match {
case Success(res) => println("Do something on sucess")
case Failure(ex) => println(s"Failed with ex: ${ex.getMessage}")
}
}
}
You can read more about Try at scala:
https://www.scala-lang.org/api/2.13.x/scala/util/Try.html