Prohibit generating of apply for case class

Question

I\'m writing a type-safe code and want to replace apply() generated for case classes with my own implementation. Here it is:

import shap         


        

Answer 1

So you can make the constructor private and ensure that T is also something different to Nothing.

I believe the best way to ensure the constructor is private (as well as many other things as @MateuszKubuszok show) is to use a (sealed) trait instead of a class:
(if you can not use a trait for whatever reasons, please refer to Mateusz's answer)

import shapeless._

sealed trait Data
final case object Remote extends Data
final case object Local extends Data

sealed trait SomeClass {
  type T <: Data
}

object SomeClass {
  type Aux[TT] = SomeClass { type T = TT }
  def apply[TT <: Data](implicit ev1: TT =:!= Data, ev2: TT =:!= Nothing): Aux[TT] =
    new SomeClass { override final type T = TT }
}

Which works like this:

SomeClass() // Does not compile.
SomeClass.apply[Remote.type] // Compiles.
SomeClass.apply[Data] // Does not compile.

You can see it running here.