CODEWITHSUNDEEP
scalaplayframework
sergeda
sergeda

Reputation: 2201

Scala strange type error in Play Framework form

I have this code:

package deliveries.NewPost
import play.api.data._
import play.api.data.Forms._

case class NewPostValidator(town: String, number: Int)

object NewPost extends Delivery{
  def form[NewPostValidator](): Form[NewPostValidator] = Form(mapping(
    "town" -> nonEmptyText,
    "number" -> number)(NewPostValidator.apply)(NewPostValidator.unapply))
}

At compile time it gives me strange error:

type mismatch; [error] found : play.api.data.Mapping[deliveries.NewPost.NewPostValidator] [error] required: play.api.data.Mapping[NewPostValidator]

Basically the same class shows with full path and without full path. What can it be?

I will clarify what I'm trying to achieve: I want every class extending trait to have method "form" that returns Form with some validator in it. For this I've created trait:

trait Delivery {
  def form[T](): Form[T]
}

and trying to implement this method in my class.

Upvotes: 1

Views: 77

Answers (1)

slouc
slouc

Reputation: 9698

Saying def form[NewPostValidator] is like saying def form[T], just with a different identifier. Compiler doesn't see the NewPostValidator in the method body as the "real" NewPostValidator, but as your made-up type NewPostValidator that you declared in def form[NewPostValidator].

Solution:

Parameterize your trait with [T] instead of your method, and have your class extend the trait with a specific type.

trait Delivery[T] {
  def form(): Form[T]
}

object NewPost extends Delivery[NewPostValidator] {
  def form(): Form[NewPostValidator] = Form(mapping(
    "town" -> nonEmptyText,
    "number" -> number)(NewPostValidator.apply)(NewPostValidator.unapply))
}

Upvotes: 1

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