Issue with specialization and higher kinds in scala

Question

I have these lines (scala 2.11.11):

trait TypeClass[T] class DoubleIsTypeClass extends TypeClass[Double] implicit val forDouble = new DoubleIsTypeClass

Know lets add the following line :

case class User[V[_], @specialized T : TypeClass](a: V[T])

Now it does not compile. Removing @specialized fixes it. Is it a bug ? I don't really need higher kinds here except their help with type inference but that is a big deal.

EDIT Just for those who may have stumbled upon a similar problem

Typeclasses are not the issue here, case classes are:

case class User[V[_], @specialized T](a: V[T])

The line above does not compile on its own.

Provide more information on "does not compile". What's the compilation error? why do you need @specialized? — Abhijit Sarkar
– Abhijit Sarkar, Commented Jul 4, 2017 at 20:07

Yuval Itzchakov · Accepted Answer · 2017-07-04 20:07:32Z

1

This looks like SI-9227. It seems to be a bug.

In general, these are some quirks around specialization which are worth reading about.

answered Jul 4, 2017 at 20:07

Yuval Itzchakov

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