Scala: What is opt keyword?

Question

What is opt keyword in following code?

import scala.util.control.Exception._
import java.net._

val s = "http://www.scala-lang.org/"
val x1 = catching(classOf[MalformedURLException]) opt new URL(s)
val x2 = catching(classOf[MalformedURLException], classOf[NullPointerException]) either new URL(s)

http://www.scala-lang.org/api/current/scala/util/control/Exception $.html

Answer 1

It's not a keyword, it's a method, defined in Catch[T] , which the result type of catching() . See its doc at http://www.scala-lang.org/api/current/index.html#scala.util.control.Exception$$Catch@opt[U%3E:T](body:=%3EU):Option[U]

The above code is equivalent to the following, where we use . syntax to call the methods opt and either :

val s = "http://www.scala-lang.org/"
val x1 = catching(classOf[MalformedURLException]).opt(new URL(s))
val x2 = catching(classOf[MalformedURLException], classOf[NullPointerException]).either(new URL(s))

Answer 2

It's not a keyword , it's a method imported from scala.util.control.Exception._ , here's its definition and Scaladoc:

/** Apply this catch logic to the supplied body, mapping the result
 *  into `Option[T]` - `None` if any exception was caught, `Some(T)` otherwise.
 */
def opt[U >: T](body: => U): Option[U] = toOption(Some(body))