A better way to test the value of an Option?

Question

I often find myself with an Option[T] for some type T and wish to test the value of the option against some value. For example:

val opt = Some("oxbow")
if (opt.isDefined && opt.get == "lakes") 
   //do something

The following code is equivalent and removes the requirement to test the existence of the value of the option

if (opt.map(_ == "lakes").getOrElse(false))
 //do something

However this seems less readable to me. Other possibilities are:

if (opt.filter(_ == "lakes").isDefined)

if (opt.find(_ == "lakes").isDefined) //uses implicit conversion to Iterable

But I don't think these clearly express the intent either which would be better as:

if (opt.isDefinedAnd(_ == "lakes"))

Has anyone got a better way of doing this test?

score 46 · Accepted Answer · answered Oct 23 '09 at 07:46

46

How about

if (opt == Some("lakes"))

This expresses the intent clearly and is straight forward.

answered Oct 23 '09 at 07:46

Walter Chang

Sometimes the simplest solution is the best :) – Ula Krukar Oct 23 '09 at 10:49
3

Won't this still compile even if `opt` is not an Option? – cdmckay Jun 24 '15 at 23:11

score 28 · Answer 2 · answered Jun 30 '14 at 17:13

28

For Scala 2.11, you can use Some(foo).contains(bar)

answered Jun 30 '14 at 17:13

marconi

That's the way I go usually. I just can't understand by this answer is not accepted as the right one. – Boris Nov 05 '20 at 08:41

score 16 · Answer 3 · answered Oct 23 '09 at 13:39

16

Walter Chang FTW, but here's another awkward alternative:

Some(2) exists (_ == 2)

answered Oct 23 '09 at 13:39

Daniel C. Sobral

4

Daniel, that is *awful*! `:-)` – oxbow_lakes Oct 23 '09 at 14:35
I actually like this; avoids one creation & an unapply, and yet is succinct – HRJ Oct 25 '09 at 07:43
2

This is actually the standard way as far as I'm concerned. – psp Oct 26 '09 at 23:54
2

It's a slight pity that Option doesn't implicitly convert to `Seq`, which would allow for `Some(1) contains 1`. – retronym Jan 16 '10 at 20:58
@retronym Yeah, but, on the other hand, `Some(2).toSeq contains 2` works. Too round-about for my tastes. – Daniel C. Sobral Jan 16 '10 at 21:43
3

Perhaps contains should be added to Option directly. – retronym Jan 17 '10 at 09:32
@retronym Not a bad idea, actually. Go to http://lampsvn.epfl.ch/trac/scala and open an enhancement ticket if you truly care about it. – Daniel C. Sobral Jan 17 '10 at 16:52
Someone else finally opened that ticket: https://issues.scala-lang.org/browse/SI-6064 – Seth Tisue Jul 11 '12 at 22:08

score 7 · Answer 4 · answered Oct 28 '09 at 03:22

7

val opt = Some("oxbow")
opt match {
  case Some("lakes") => //Doing something
  case _ => //If it doesn't match
}

answered Oct 28 '09 at 03:22

Ken Bloom

score 3 · Answer 5 · answered Oct 23 '09 at 10:05

3

You can use for-comprehension as well:

for {val v <- opt if v == "lakes"}
  // do smth with v

answered Oct 23 '09 at 10:05

Alexander Azarov

score -1 · Answer 6 · answered Oct 23 '09 at 10:14

-1

I think pattern matching could also be used. That way you extract the interesting value directly:

val opt = Some("oxbow")
opt match {
  case Some(value) => println(value) //Doing something
}

answered Oct 23 '09 at 10:14

Jostein Stuhaug

This does not test against the value - only that it is present. The reason I want to avoid a `match` is that this consequently results in the `else` logic residing in multiple places (i.e. the `case None` and if the value is not the desired one) – oxbow_lakes Oct 23 '09 at 15:34

6 Answers6