Using scala.util.control.Exception

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Indeed – I also find it pretty confusing! Here’s a problem where I have some property which may be a parseable date:

def parse(s: String) : Date = new SimpleDateFormat("yyyy-MM-dd").parse(s)
def parseDate = parse(System.getProperty("foo.bar"))

type PE = ParseException
import scala.util.control.Exception._

val d1 = try { 
             parseDate
           } catch { 
             case e: PE => new Date
           }

Switching this to a functional form:

val date =
     catching(classOf[PE]) either parseDate fold (_ => new Date, identity(_) )

In the above code, turns catching(t) either expr will result in an Either[T, E] where T is the throwable’s type and E is the expression’s type. This can then be converted to a specific value via a fold.

Or another version again:

val date =
     handling(classOf[PE]) by (_ => new Date) apply parseDate

This is perhaps a little clearer – the following are equivalent: 

handling(t) by g apply f 
try { f } catch { case _ : t => g }

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