Restrict Constructor Access

Question

I have a type like this

sealed class Foo[A](val value: A)

object Foo {
    def apply[A](v: A)(implicit num: Numeric[A]): Foo[A] =
      /* highly complex stuff to make a Foo[A] */

    implicit def toA[A](x: Foo[A]) = x.value
}

Foo as a class is only supposed to hold the value, so an implicit Numeric would not make much sense. But I need the type of A to be always a numeric.

So my idea is to just make it impossible to use Foos normal constructor outside of its companion. Is that possible in Scala?

Answer 1

Yeah, since the companion object can access private members of its companion class you can just make the primary (and auxiliary if any) constructor private. Pseudo code here:

class ConcreteFoo private (n: Int) extends Foo(n)