CODEWITHSUNDEEP
scala
GammaVega
GammaVega

Reputation: 779

How to return different collection with yield statement

Based on my limited knowledge i know compiler automatically inherits the collection return type and based on that it determines the type of collection to return so in below code i want to return Option[Vector[String]].

I tried to experiment with below code and i get compilation error

type mismatch;  found   : scala.collection.immutable.Vector[String]  required: Option[Vector[String]]

Code:

def readDocument(v:Option[Vector[String]]) : Option[Vector[String]] =    
{
   for ( a <- v;  
   b <- a )
     yield 
     {
        b
     }
}

Upvotes: 0

Views: 142

Answers (3)

john sullivan
john sullivan

Reputation: 1978

How about this?

  def readDocument(ovs: Option[Vector[String]]): Option[Vector[String]] =
    for (vs <- ovs) yield for (s <- vs) yield s

Upvotes: 0

kiritsuku
kiritsuku

Reputation: 53348

scala> for (v <- Some(Vector("abc")); e <- v) yield e
<console>:8: error: type mismatch;
 found   : scala.collection.immutable.Vector[String]
 required: Option[?]
              for (v <- Some(Vector("abc")); e <- v) yield e
                                               ^

scala> for (v <- Some(Vector("abc")); e = v) yield e
res1: Option[scala.collection.immutable.Vector[String]] = Some(Vector(abc))

A nested x <- xs means flatMap and will work only when the returned type is the same type as the most outer one.

Upvotes: 2

korefn
korefn

Reputation: 955

The for comprehension already unboxes for you Option so this should work

def readDocument(v:Option[Vector[String]]) : Option[Vector[String]] =    
{
  for ( a <- v )
  yield 
  {
    a
  }
}

Upvotes: 0

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