Scala: Implementing a subtype of Numeric[T]

Question

How does one go about implementing a subtype of Numeric[T]? I have been looking for at guide on this but haven't found any. Example of subtypes could be Rational or Complex?

Thanks in advance Troels

Peregrinate

Are you trying to create an instance of Numeric for a specific T, (e.g. ComplexNumeric), or a more general numeric type, (e.g. Real[T])? – Buntline

Well I guess what I want is an instance of Numeric. My big problem is that I haven't been able to find a guide documentation on how to benefit from the new Numeric[T] type. Does such a guide exist? – Peregrinate

Answer 1

An absolutely useless String Numeric:

trait StringIsNumeric extends Numeric[String] {
  def plus(x: String, y: String): String = "%s+%s" format (x, y)
  def minus(x: String, y: String): String = "%s-%s" format (x)
  def times(x: String, y: String): String = "%s*%s" format (x, y)
  def quot(x: String, y: String): String = "%s/%s" format (x, y)
  def rem(x: String, y: String): String =  "%s%%s" format (x, y)
  def negate(x: String): String = "-%s" format (x)
  def fromInt(x: Int): String = x.toString
  def toInt(x: String): Int = 0
  def toLong(x: String): Long = 0L
  def toFloat(x: String): Float = 0.0f
  def toDouble(x: String): Double = 0.0
}
implicit object StringIsNumeric extends StringIsNumeric with Ordering.StringOrdering


def x[T: Numeric](t1 : T, t2 : T)  = {
  val n = implicitly[Numeric[T]]
  import n._
  t1 * t2
}
scala> x("a","b")
res0: java.lang.String = a*b

Land

Answer 2

I added Real to Scalaz, with instances Real[Double] and Real[Dual].

I found it convenient to make fromDouble implicit

Buntline