CODEWITHSUNDEEP
scala
user79074
user79074

Reputation: 5270

collectFirst with match clause in partial function

I am wondering if and how I can use a match clause within a collectFirst clause in scala. So for example I want to do something like the following:

myCollection collectFirst {
  case i =>
    otherCollection.find(_ == i + 1) match {
      case Some(j) => j
      case None => // Check the next i???
  }
}

Note I know I could achieve the above logic without the match clause but am doing it this way purely for explanatory purposes

Upvotes: 0

Views: 1642

Answers (2)

user79074
user79074

Reputation: 5270

I defined a function as follows:

def mapFirst[A, B](seq: Seq[A])(f: A => Option[B]): Option[B] = seq match {
  case Seq(a, rest @ _ *) =>
    f(a) match {
      case Some(b) => Some(b)
      case None => mapFirst(rest)(f)
    }
    case _ => None
}

Which could be used thus:

  mapFirst(myCollection) { i => 
    otherCollection.find(_ == i + 1) match {
      case Some(j) => Some(j)
      case None => None
    }
  }

Upvotes: 0

j-keck
j-keck

Reputation: 1031

like this?

val other = List(4)
List(1, 2, 3, 4) collectFirst {
  case i if other.contains(i) => s"other has $i"
}

res0: Option[String] = Some(other has 4)

Note I know I could achieve the above logic without the match clause but am doing it this way purely for explanatory purposes

List(1, 2, 3, 4) collectFirst {
  case i if (other.find(_ == i) match {
    case Some(_) => true
    case None => false
  }) => s"other has $i"
}

don't do that in your code!

Upvotes: 1

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