Using scala.util.control.Exception

Question

Does anybody have good examples of using scala.util.control.Exception version 2.12.0 (version 2.8.0), ? I am struggling to figure it out from the types.

Answer 1

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 }