Scala Sugar for Options of Seq

Question

I need to map a sequence, and if empty consider it a None rather than a empty sequence. So :

val quote_ =
quote_inner_element.map( q=> {
  val quote_link_regex(quote_link_id) = q.attr("href")
  Quote(quote_link_id.toInt)
})
val quote = if(quote_.isEmpty) None else Some(quote_)

I hate having to define two variables. If I do

val quote = Option(
quote_inner_element.map( q=> {
  val quote_link_regex(quote_link_id) = q.attr("href")
  Quote(quote_link_id.toInt)
}))

Since I get tons of Some(Seq()). What's the sugar, sugar daddies ?

By the way, it is generally considered better to use camelCase for Scala identifiers than underscores. — Robin Green, Nov 16 '13 at 12:01
If you want to have a type where you either have an empty sequence, or a non-empty sequence... why don't you just use `Seq`, instead of `Option[Seq]`? What does this give you, except reduced type safety, which is bad? — Robin Green, Nov 16 '13 at 12:03
It would be nice if you could provide the code as an encapsulated method so that people can see all the corresponding types. makes it easier (at least for me:P) to read. — Stefan Kunze, Nov 16 '13 at 12:05
Scalaz approach which encodes that you have performed this transformation (and thus your following code does not need to check again and again): `val quote = q.toNel` (`: Option[NonEmptyList[T]]`). — Debilski, Nov 16 '13 at 15:28

flavian · Answer 1 · 2013-11-16T14:57:08.480

2

implicit class SeqAugment[T](val s: Seq[T]) {
   final def toOption: Option[Seq[T]] = if (s.isEmpty) None else Some(s);
}
val s = Seq(1, 2, 3);
s.toOption

edited Nov 16 '13 at 14:57

answered Nov 16 '13 at 11:49

flavian

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Did you mean "extends AnyVal", for creating a value class? – Knut Arne Vedaa Nov 16 '13 at 12:01
I think you're mixing the concepts. See e.g. http://www.blog.project13.pl/index.php/coding/1769/scala-2-10-and-why-you-will-love-implicit-value-classes/ – Knut Arne Vedaa Nov 16 '13 at 14:35
1

Implicit classes and value classes http://docs.scala-lang.org/overviews/core/value-classes.html are orthogonal features, but they can be combined. – Knut Arne Vedaa Nov 16 '13 at 15:04

Knut Arne Vedaa · Accepted Answer · 2013-11-16T15:10:56.247

2

You can avoid creating two top-level vals in several ways:

Using an inner val:

val quote = {
  val quote = fooQuote map(q => myFunc(q))
  if (quote.isEmpty) None else Some(quote)
}

Note that even if the val names are identical, they don't refer to the same value; the inner one shadows the outer.

Using a match expresssion:

val quote = fooQuote map(q => myFunc(q)) match { case q => if (q.isEmpty) None else Some(q) }

edited Nov 16 '13 at 15:10

answered Nov 16 '13 at 12:00

Knut Arne Vedaa

15,372
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as I can't test it currently something strikes me this could be further improved by using reduceleftoption? – Stefan Kunze Nov 16 '13 at 12:03

Scala Sugar for Options of Seq

2 Answers2