CODEWITHSUNDEEP
scalagenerics
Imran
Imran

Reputation: 181

Scala: Why the Int type list contains String as well?

val wordList = List("I", "want", "to", "learn", "scala")
val wordSizeList = list.map(x=>x.length)
def func[A, B](a:List[A]):List[B]={
  a.collect({case x:B => x})
}

val result = func[Any, Int](wordList ::: wordSizeList)

Below is the worksheet result

wordList: List[String] = List(I, want, to, learn, scala)
wordSizeList: List[Int] = List(1, 4, 2, 5, 5)
func: [A, B](a: List[A])List[B]

result: List[Int] = List(I, want, to, learn, scala, 1, 4, 2, 5, 5)

why doesn't it filter based on the Generic type "B"? And if you see the result list, how can a Int type list can contain String as well?

Upvotes: 2

Views: 73

Answers (1)

Leo C
Leo C

Reputation: 22449

Looks to me a type erasure problem, which can be remedied with a ClassTag:

import scala.reflect.ClassTag

def func[A, B : ClassTag](a: List[A]): List[B] = {
  a.collect{ case x: B => x }
}

val result = func[Any, Int](wordList ::: wordSizeList)
// result: List[Int] = List(1, 4, 2, 5, 5)

Upvotes: 6

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