Unexpected behavior when creating Scala Option from java.lang.Long

Question

Given following code:

val javaLong: java.lang.Long = null
val opt: Option[Long] = Option(javaLong)

I expected opt to be None but for some reason it is Some(0). I also found this bug and it appears that implicit conversion happens before option's apply method. I think this is still a bug because one wouldn't expect that behavior and I am wondering is there any workaround or some better ways to wrap nulls.

Update: The code above is only a simplified piece. The real example is something like:

Person(Option(doc.getLong()))

where Person is:

 case class Person(id: Option[Long])

and method doc.getLong() is java method that returns java.lang.Long

jub0bs · Accepted Answer · 2018-10-10 20:47:51Z

3

The conversion to Option[Long] is actually not just a conversion to an Option but also an implicit cast to Scala's Long from Java's Long.

val javaLong: java.lang.Long = null
// javaLong: Long = null

val long: java.lang.Long = javaLong
// long: Long = null
val long: Long = javaLong
// long: Long = 0

First we have the implicit conversion from Java's Long to Scala's Long which apparently produces 0 out of null.

Only then do we have the conversion to an Option.

If we specify Java's Long as a type of our Option then we do get None and not Some(0):

val opt: Option[java.lang.Long] = Option(javaLong)
// opt: Option[Long] = None (here it's Java's Long)

And we can finally cast the Option[java.lang.Long] to use Scala's Long:

val opt: Option[Long] = Option(javaLong).map(_.toLong)
// opt: Option[Long] = None (here it's Scala's Long)

edited Oct 10, 2018 at 20:47

jub0bs

67.2k27 gold badges198 silver badges200 bronze badges

answered Oct 10, 2018 at 16:40

Xavier Guihot

62.8k26 gold badges320 silver badges202 bronze badges

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

6 Comments

Dmitry K Over a year ago

Yes, but the problem appears when it used in single line code in constructor. I updated the question

Xavier Guihot Over a year ago

You might want to create an intermediate variable

Dmitry K Over a year ago

I think it won't help. val l:Long = javaLong will produce 0. And Option[java.lang.Long] is not the same as Option[Long]

Xavier Guihot Over a year ago

You can map the resulting Option[java.lang.Long] to Scala's Long: Option(javaLong).map(_.toLong). Person(Option(javaLong).map(_.toLong)) results in Person(None)

Tim Over a year ago

Option is working as expected, the oddity is expecting java.lang.Long and Long to be the same when one can be null and the other can't! You would have the same problem with any generic that tested for null values.

|

Collectives™ on Stack Overflow

Unexpected behavior when creating Scala Option from java.lang.Long

1 Answer 1

6 Comments

Your Answer

Hot Network Questions

Collectives™ on Stack Overflow

1 Answer 1

6 Comments

Your Answer

Sign up or log in

Post as a guest

Related