CODEWITHSUNDEEP
scala
user3483203
user3483203

Reputation: 51165

Scala type mismatch with Traversables

I am trying to write a function that takes an Traversable of functions, and a Traversable of values, and returns a Traversable of functions applied to those values. I am getting a type mismatch error when I try to call the function on a list and a vector. Here is my code:

def applyFunctions[A](x: Traversable[A => A], y: Traversable[A]): Traversable[A] = {
  for (ys <- y; 
       xs <- x
       ) yield (xs(ys))
}

And then I try and call this function using this:

transform(List({(x: Double) => x + x}, {(x: Double) => x * 2}), Vector(1,2,3))

And I get the following error:

error: type mismatch;
 found   : List[Double => Double]
 required: Traversable[AnyVal => AnyVal]

I thought that List was a subclass of Traversable, so I could able to use Traversable in the function definition. Any help would be appreciated.

Upvotes: 1

Views: 160

Answers (2)

Marcin Sucharski
Marcin Sucharski

Reputation: 1231

Type parameter A is deduced from all arguments of function. Your first argument has type List[Double => Double] however second argument is of type Vector[Int]. Common ancestor of Double (A from first argument) and Int (A from second argument) is AnyVal and that's why it is final value of A.

To fix your issue, change Vector(1,2,3) to Vector(1.0,2.0,3.0).

Upvotes: 0

akuiper
akuiper

Reputation: 215037

The Vector is interpreted as Vector[Int], you can declare it as Vector[Double] since it should have the same type as the type A in the functions, which is Double:

applyFunctions(List({(x: Double) => x + x}, {(x: Double) => x * 2}), Vector[Double](1,2,3))
// res9: Traversable[Double] = Vector(2.0, 2.0, 4.0, 4.0, 6.0, 6.0)

Upvotes: 1

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