Scala Option - Getting rid of if (opt.isDefined) {}

Question

My code is becoming littered with the following code pattern:

val opt = somethingReturningAnOpt
if (opt.isDefinedAt) {
    val actualThingIWant = opt.get
}

Is there some way to simplify this? (it seems needlessly complex and a code smell). Ideally it would be something like:

if (Some(actualThingIWant) = somethingReturningAnOpt) {
   doSomethingWith(actualThingIWant)
}

Is anything like that possible?

That looks awfully close to `match` trying to use `if` syntax... any grudge against the former? Also, don't forget that Option is usable in `for` as well... — , Dec 08 '11 at 07:00
[This old thread](http://stackoverflow.com/questions/2079170/why-optiont) may be of some help. — missingfaktor, Dec 08 '11 at 08:13
The for syntax looks almost perfect - but my only qualm is that it is unintuitive and may give the impression to someone else on the codebase that it is looping over something rather than performing a conditional operation. — laurencer, Dec 08 '11 at 22:42

score 38 · Accepted Answer · answered Dec 08 '11 at 07:02

38

Maybe something like this:

somethingReturningAnOpt match {
  case Some(actualThingIWant) => doSomethingWith(actualThingIWant)
  case None =>
}

or as pst suggests:

somethingReturningAnOpt.foreach { actualThingIWant =>
  doSomethingWith(actualThingIWant)
}

// or...

for (actualThingIWant <- somethingReturningAnOpt) {
  doSomethingWith(actualThingIWant)
}

answered Dec 08 '11 at 07:02

Rogach

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It's worth noting that the for syntax allows to easily chain and compose option call: val optRes = for { res1 <- getOptRes1 ; res2 <- getOptRes2 } yield { doSomething(res1,res2) } /* here, res1 and res2 are not option, but the content, if available, and optRes will be an Option[TypeOfDoSomethingReturn] */ – fanf42 Dec 08 '11 at 08:53

score 33 · Answer 2 · edited Feb 27 '14 at 19:28

33

The canonical guide to Option wrangling is by Tony Morris.

edited Feb 27 '14 at 19:28

Ben Regenspan

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answered Dec 08 '11 at 07:55

Duncan McGregor

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Personally I find case statements to be clearer for most situations; I'm not sure why Tony discourages them. – Dan Burton Dec 08 '11 at 17:14
1

I happen to agree with both comments! – Duncan McGregor Dec 09 '11 at 00:16
This looks like a link only answer. Can you quote from the article, to make it more useful (and bring it up todays site standard)? – Suma Mar 31 '21 at 08:43
Frankly, no. But if you want to add value to the world by paraphrasing someone else’s content just so that other people don’t have to click a link, please fill yer boots. – Duncan McGregor Apr 01 '21 at 18:24

score 10 · Answer 3 · answered Dec 08 '11 at 07:17

10

Or:

somethingReturningAnOpt.map(doSomethingWith(_))

As in in:

val str = Some("foo")
str.map(_.toUpperCase)

... and use flatMap when the result of doSomethingWith is an Option itself.

val index = Option(Map("foo" -> "bar"))
index.flatMap(_.get("whatever"))        // Returns None :-)
index.map(_.get("whatever"))            // Returns Some(None) :-(

answered Dec 08 '11 at 07:17

Wilfred Springer

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You could even shorten that to `somethingReturningAnOpt.map(doSomethingWith)`, no? – cdmckay Jan 25 '14 at 22:25
I think this is the correct way to use Option monad – TlmaK0 Nov 21 '14 at 14:34
This can only be used if the operation to execute for Some actually returns a value. – andresp Sep 16 '17 at 13:42

score 5 · Answer 4 · answered Dec 08 '11 at 09:17

The following code cannot do something useful, since after the if, actualThingIWant is not always defined and as such this code will not compile, as long as you try to use actualThingIWant later.

val opt = somethingReturningAnOpt
if (opt.isDefinedAt) {
    val actualThingIWant = opt.get
}

So, you have to provide a default value. This can be achieved with getOrElse:

val thingIWant = opt.getOrElse(myDefaultValue)

Or if you don't want to have actualThingIWant after the body of the if, which means you want to trigger some side-effects only if the option is defined, you can write:

opt.foreach{ thingIWant => 
  println(thingIWant)
}

or a bit shorter

opt.foreach(println)

Scala Option - Getting rid of if (opt.isDefined) {}

4 Answers4