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?

Solution 1

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)
}

Solution 2

The canonical guide to Option wrangling is by Tony Morris.

Solution 3

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) :-(

Solution 4

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)

View more solutions

Comments

[fanf42]

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] */

[Dan Burton]

Personally I find case statements to be clearer for most situations; I'm not sure why Tony discourages them.

[Duncan McGregor]

I happen to agree with both comments!

[cdmckay]

You could even shorten that to somethingReturningAnOpt.map(doSomethingWith), no?

[TlmaK0]

I think this is the correct way to use Option monad

[andresp]

This can only be used if the operation to execute for Some actually returns a value.

[Suma]

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)?

[Duncan McGregor]

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.