Using either for error handling in return

Question

I'm currently making a function that returns an object. But if I find something invalid in the input I want to return something to indicate that problem. I just can not wrap my head around on working this out.. What is the correct way to handle errors here? Using Options? But returning None does not specify any specific problems.

case class myClass(value: Int)
def myFunction(input: Int) : myClass
{
  //return myClass if succeded
  //else return some error - what do I return here? 
}


//I've read that to handle some error scenarios you should do something like this:
sealed trait SomeError
object SomeError{
  case object UnknownValue extends SomeError
  case object SomeOtherError extends SomeError
  case object OutOfBounds extends SomeError
}
//But how do I return myClass and this at the same time in case of an error?

joel · Accepted Answer · 2018-07-02 13:33:42Z

5

It's true, Option can't give you details about your error. For that you can use Either which is more flexible. Either is extended by Left and Right. On success, one returns a Right, on failure a Left (by convention).

e.g.

sealed trait MyTrait
case class MyClass(value: Int) extends MyTrait

def myFunction(input: Int): Either[String, MyTrait] = {
  if (input >= 0) Right(MyClass(input)) else Left("input was negative")
}

Or using SomeError,

def myFunction(input: Int): Either[SomeError, MyTrait] = {
  if (input >= 0) Right(MyClass(input)) else Left(OutOfBounds)
}

edited Jul 2, 2018 at 13:33

answered Jul 2, 2018 at 12:44

joel

8,1225 gold badges43 silver badges75 bronze badges

Sign up to request clarification or add additional context in comments.

2 Comments

JoeDortman Over a year ago

Oh okay! So using Either should, in this case, use 'myClass'(left) and 'SomeError'(right)? ^^

Andrey Tyukin Over a year ago

@JoeDortman No. Either is right-biased, so you should use Right for the "correct" results, and Left for "improvement proposals".

Collectives™ on Stack Overflow

Using either for error handling in return

1 Answer 1

2 Comments

Your Answer

Linked

Hot Network Questions

Collectives™ on Stack Overflow

1 Answer 1

2 Comments

Your Answer

Sign up or log in

Post as a guest

Linked

Related