Exception

We can define the exception class.

class BadInput(msg: String) extends Exception(msg)

to use it,

throw BadInput("missing data")

We use try catch to handle exceptions.

def validatedInput(): String =
  try getInput()
  catch
    case BadInput(msg) =>
      println(msg)
      validatedInput()
    case ex: Exception =>
      println("fatal error")
      throw ex

Shortcoming of try/catch

• They don't show up in the types of functions that throw them.

• They don't work in parallel computations where we want to communicate an exception from one thread to another.

Try Type

To overcome the shortage of try/catch, we come up with Try.

It resembles to Option

abstract class Try[+T]
case class Success[+T](x: T) extends Try[T]
case class Failure(ex: Exception) extends Try[Nothing]