CODEWITHSUNDEEP
scalascala-collections
Maciej
Maciej

Reputation: 145

simple type mismatch error

I was trying to write some simple method toList...

trait Stream[+A] {

  def uncons: Option[(A, Stream[A])]

  def isEmpty: Boolean = uncons.isEmpty

  def toList[A]: List[A] = this.uncons match {
    case Some((h,t)) => h::t.toList
    case None => List()
  }

}

however, this results in the following error:

type mismatch; found : x$1.type (with underlying type A) required: A

I don't understand why this code doesn't work. Probably I am missing something very obvious :(

Upvotes: 1

Views: 228

Answers (1)

virsox
virsox

Reputation: 463

The problem is in your toList method definition. By doing:

def toList[A]: List[A] = this.uncons match { ... }

You are actually defining a new type A in which your method is parameterized. Just declare the method as:

def toList: List[A] = this.uncons match { ... }

and you are good to go (this definition would be using the same A defined in the class)

Upvotes: 5

Related Questions