How do I ignore an exception?

Question

Is there more elegant way to write the following?

try {
    ... // Some throwing code
    return first
} 
catch {
    case e:ExceptionType => {} // No code to execute. Ignore error.
}
return second

score 46 · Accepted Answer · answered Oct 18 '10 at 15:48

46

scala.util.control.Exception.ignoring(classOf[ExceptionType]) {
  ... // Some throwing code
}

answered Oct 18 '10 at 15:48

Daniel C. Sobral

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How to do in case the throwing code has to return a value? – Galuoises Mar 10 '21 at 18:36

Rex Kerr · Answer 2 · 2011-02-20T21:06:58.303

@Daniel has already provided the canonical method to use to do this. Look through the other methods in scala.util.control.Exception--they are quite helpful and generic!

If you need to get a return value out of the try block, use failing instead of ignoring (but be aware that the result is an Any, i.e. not typesafe).

You can also write your own exception-catcher, which will be a little slow for heavy-duty work but otherwise nice to use:

class DefaultOn[E <: Exception] {
  def apply[A](default: => A)(f: => A)(implicit m: Manifest[E]) = {
    try { f } catch { case x if (m.erasure.isInstance(x)) => default }
  }
}
object DefaultOn { def apply[E <: Exception] = new DefaultOn[E] }

scala> DefaultOn[NumberFormatException](0) { "Hi".toInt }
res0: Int = 0

Or if you like options:

class TryOption[E <: Exception] {
  def apply[A](f: => A)(implicit m: Manifest[E]) = {
    try { Some(f) } catch { case x if (m.erasure.isInstance(x)) => None }
  }
}
object TryOption { def apply[E <: Exception] = new TryOption[E] }

scala> TryOption[NumberFormatException] { "Hi".toInt }
res1: Option[Int] = None

Or you can be inspired by this plus the library routines and create your own methods to ignore multiple different exceptions and preserve types on the return value.

BTW it could be written a bit shorter with `handling(classOf[NumberFormatException]).by(_ => 0) { "Hi".toInt }` — Qrilka, Feb 21 '11 at 20:16

Vasil Remeniuk · Answer 3 · 2010-10-18T15:32:28.140

5

In Scala all exceptions are not checked, so if you don't want, you may just skip handling them (and thus exception will be escalated to a higher level). Silently ignoring an exception the way you want to do is generally a bad practice. However, your code can be shortened to:

try {
  ... // Some throwing code
} catch {
  case e:ExceptionType => 
}

edited Oct 18 '10 at 15:32

answered Oct 18 '10 at 15:04

Vasil Remeniuk

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score 2 · Answer 4 · answered Apr 06 '17 at 08:31

2

Hows about:

Try { 
     // some throwing code 
}

This will ignore all non fatal exceptions, which is what you want to do most of the time.

answered Apr 06 '17 at 08:31

jonathanChap

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What do you mean by non-fatal exceptions? – Basilevs Apr 06 '17 at 10:22
Have a look at the source for Try, it calls NonFatal, which considers VirtualMachineError, ThreadDeath, InterruptedException, LinkageError and ControlThrowable to be fatal – jonathanChap Apr 07 '17 at 05:55
This is not accurate. As of Scala 2.11, this would give a warning at compile time: "A try without a catch or finally is equivalent to putting its body in a block; no exceptions are handled." Indeed, it is identical to not using the Try at all. You have to add a catch to catch NonFatal exceptions, ie catch{case NonFatal(e)=>} – TaylerJones Jul 28 '17 at 21:55
1

you're confusing try with Try - which is the main problem with this method of ignoring exceptions – jonathanChap Jul 31 '17 at 09:39

How do I ignore an exception?

4 Answers4