How do I make a class generic for all Numeric Types?

Question

I am trying to create a Vector class that is generic for all numeric types. my original attempt was to write a class for all Types like this:

class Vector3f(         


        

Answer 1

You can't. Not right now. Maybe when, and if, Numeric gets specialized.

Say you get the simplest parameterized class possible:

class Vector3[@specialized T](val x: T, val y: T, val z: T)(implicit num: Numeric[T]) {
    def +(other: Vector3[T]) = new Vector3(num.plus(x, other.x), num.plus(y, other.y), num.plus(z, other.z))
}

The method + will compile into something roughly like this:

override  def +$mcD$sp(other: Vector3): Vector3 = new Vector3$mcD$sp(
  scala.Double.unbox(
    Vector3$mcD$sp.this.Vector3$$num.plus(
      scala.Double.box(Vector3$mcD$sp.this.x()), 
      scala.Double.box(other.x$mcD$sp()))),
  scala.Double.unbox(
    Vector3$mcD$sp.this.Vector3$$num.plus(
      scala.Double.box(Vector3$mcD$sp.this.y()),
      scala.Double.box(other.y$mcD$sp()))),
  scala.Double.unbox(
    Vector3$mcD$sp.this.Vector3$$num.plus(
      scala.Double.box(Vector3$mcD$sp.this.z()), 
      scala.Double.box(other.z$mcD$sp()))), 
  Vector3$mcD$sp.this.Vector3$$num);

That's scalac -optimize -Xprint:jvm output. Now there are even subclasses for each specialized type, so that you can initialize a Vector3 without boxing, but as long as Numeric is not specialized, you can't go further.

Well... you can write your own Numeric and specialize that, but, at that point, I'm not sure what you are gaining by making the class parameterized in first place.