CODEWITHSUNDEEP
scala
Jessica
Jessica

Reputation: 2425

Replacing options in Scala with default values if there is nothing there

Suppose I have an item of the type (Option[Long], Option[Long], Option[Long], Option[Long], Option[Long]), and I want to convert it to an item of type (Long, Long, Long, Long, Long). I want each coordinate to contain the value of the option (if the option contains a "Some" value), or be zero otherwise.

Usually if I have an item of type Option[Long], I'd do something like

item match {
    case Some(n) => n
    case None => 0
}

But I can't do that with a 5 coordinate item unless I want to list out all 32 possibilities. What can I do instead?

Upvotes: 1

Views: 1713

Answers (4)

Peter Neyens
Peter Neyens

Reputation: 9820

Using Shapeless you could do:

import shapeless._
import syntax.std.tuple._
import poly._

object defaultValue extends Poly1 {
  implicit def defaultOptionLong = at[Option[Long]](_.getOrElse(0L))
}

val tuple : (Option[Long], Option[Long], Option[Long], Option[Long], Option[Long]) = 
  (Some(1L), None, Some(3L), Some(4L), None)

tuple.map(defaultValue)
// (Long, Long, Long, Long, Long) = (1,0,3,4,0)

You need to explicitly specify type Option[Int] if you don't use Option.apply (see this question).

(Option(1L), Option(2L)).map(defaultValue) 
// (Long, Long) = (1,2)

(Some(3L), Some(4L)).map(defaulValue) // does not compile
val t : (Option[Long], Option[Long]) = (Some(3L), Some(4L))
t.map(defaultValue) 
// (Long, Long) = (3,4)

(Option(5), None).map(defaultValue) // does not compile
val t2 (Option[Long], Option[Long]) = (Option(5), None)
t2.map(defaultValue) 
// (Long, Long) = (5,0)

We could also provide default values for other types:

object defaultValue extends Poly1 {
  implicit def caseLong = at[Option[Long]](_.getOrElse(0L))
  implicit def caseInt = at[Option[Int]](_.getOrElse(0))
  implicit def caseString = at[Option[String]](_.getOrElse("scala"))
}

val tuple2 : (Option[Int], Option[Long], Option[String]) = (None, None, None)
tuple2.map(defaultValue)
// (Int, Long, String) = (0,0,scala)

Edit: The problem with the need of explicit declaration of Some(5L) as Option[Long] can be solved using generics in the poly function :

objec defaultValue extends Poly1 {
  implicit def caseLong[L <: Option[Long]] = at[L](_.getOrElse(0L))
  implicit def caseInt[I <: Option[Int]] = at[I](_.getOrElse(0))
  implicit def caseString[S <: Option[String]] = at[S](_.getOrElse("scala"))
}

(Some("A"), Some(1), None: Option[Int], None: Option[String]).map(defaultValue)
// (String, Int, Int, String) = (A,1,0,scala)

Upvotes: 2

maks
maks

Reputation: 6006

Another possible solution:

item.productIterator.collect{
   case Some(a: Int) => a
   case _            => 0
}.toList match {
    case List(a,b,c,d,e) => (a,b,c,d,e)
    case _ => (0,0,0,0,0) //or throw exception depending on your logic
}

Upvotes: 1

Ryan
Ryan

Reputation: 7247

Simple solution:

item match {
  case (a, b, c, d, e) => (a.getOrElse(0), b.getOrElse(0), c.getOrElse(0), d.getOrElse(0), e.getOrElse(0))
}

Obviously this isn't very generic. For that you'll probably want to look at Shapeless but I'll leave that answer to the resident experts. ;)

Upvotes: 4

Jean Logeart
Jean Logeart

Reputation: 53819

You can simply do:

val res = for {
   a <- item._1.orElse(0L)
   b <- item._2.orElse(0L)
   c <- item._3.orElse(0L)
   d <- item._4.orElse(0L)
   e <- item._5.orElse(0L)
} yield (a, b, c, d, e)

Not the nicest but easy to implement and understand.

Upvotes: 1

Related Questions