CODEWITHSUNDEEP
scalascala-option
joesan
joesan

Reputation: 15435

Check for None in Scala Option type isEmpty method

I'm using the Option Type's isEmpty method to check if there is no value. I do not want to use the case match as in my situation, I just want to check if there is None as I would throw an error to the caller. But the isEmpty method fails even though the value is None.

Here is what I tried!

val questionOption = Question.getQuestionForQuestionId(userExam.get.examId, currQuesId + 1)

if(questionOption.isEmpty) {
    Left(Failure(FailureCode.NO_DATA_FOUND, "Cannot get next exam question you tampered your cookie or cookie is lost.... >> TODO... modify the exception message"))
}

It is not getting inside the if condition. I tried to do a println on the questionOption and it prints None. So wondering why I'm not getting inside the if condition.

Upvotes: 26

Views: 72046

Answers (2)

wheaties
wheaties

Reputation: 35980

From the comment under the question, the real problem emerges:

 val questionOption = Question.getQuestionForQuestionId(userExam.get.examId, currQuesId + 1) 
 if(questionOption.isEmpty) { 
   Left(Failure(FailureCode.NO_DATA_FOUND, "Cannot get next exam question you tampered your cookie or cookie is lost.... >> TODO... modify the exception message")) 
 }

By itself, if returns type Unit so that your statement is returning nothing useful. If you want to return something you need to add in either an else which then returns the least upper bound of the result types. Hence

 >>> val yo = if(1 != 0) 4
 yo: Unit

 >>> val ya = if(1 != 0) Left(1) else Right("got it")
 ya: Either[Int, String]

Upvotes: 25

axiopisty
axiopisty

Reputation: 5146

You could just do a boolean check to see of the value is None and throw the error to the caller if it is, otherwise continue processing:

scala> val o: Option[Any] = None
o: Option[Any] = None

scala> println(o == None)
true

scala> println(o != None)
false

But maybe a better way to accomplish what you're trying to do, alert the caller of the error or continue processing, would be to use Scala's Try idiom to handle errors.

Upvotes: 16

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