How to specify default value when extracting Option from Option case class

Question

If I have a case class defined as:

case class Foo(bar: Option[String])

and a variable baz: Option[Foo], what's the most idiomatic way to extract bar from baz while providing a default value like an empty string?

Right now, I have

baz.fold("")(_.bar.getOrElse(""))

but having the empty string in there twice makes me think there's a better way.

Do *not* use `getOrElse`. See my answer to a previous question for more details: http://stackoverflow.com/questions/21923600/scala-option-map-vs-pattern-matching/21936653#21936653 — vptheron, Jun 18 '14 at 17:06
I actually never noticed that `getOrElse` didn't force you to use the same type that's inside the `Option`. Why was it designed that way? — mplis, Jun 19 '14 at 16:26
This is due to the covariance of the type parameter A in `Option[+A]`. There are a lot of resources to read more about that, one example: http://stackoverflow.com/questions/14584830/covariant-type-t-occurs-in-contravariant-position — vptheron, Jun 19 '14 at 17:11

Michael Zajac · Accepted Answer · 2014-06-18T17:49:38.693

6

How about:

baz.flatMap(_.bar).getOrElse("")

Or per @vptheron's comment:

baz.flatMap(_.bar).fold("")(identity)

edited Jun 18 '14 at 17:49

answered Jun 18 '14 at 17:05

Michael Zajac

`x => x` is already defined in `Predef` under the name `identity`. – Jörg W Mittag Jun 18 '14 at 17:32
@vptheron's comments about `getOrElse` are well taken, but I actually prefer the first solution because I think the intention is clearer. – mplis Jun 19 '14 at 16:27

1 Answers1