value - is not a member of type parameter T | Scala Error - scala

Question

I am using Scala 2.13.
I wrote the following code representing a 2D Point which works on only scala.math.Numeric types:
class Point[T: Numeric](val x: T, val y: T) {
def getDistance(otherPoint: Point[T]): Double = {
math.sqrt(math.pow(otherPoint.x - x, 2) + math.pow(otherPoint.y - y, 2))
}
override def toString = "(" + x + "," + y + ")"
}
in the 4th line, I get the error "value - is not a member of type parameter T", click to see the location where error occurs:
click to see error location
Where am I going wrong here? (I am new to generics, type bounds in scala)

Answer 1

Problem 1:
To use mathematical operators given a Numeric bound, you need to
import Numeric.Implicits._
(and Fractional/Integral.Implicits._ to get division operations). Without it you need to do something like
Numeric[T].minus(otherPoint.x, x)
or to give a name to the implicit Numeric parameter instead of using a context bound. With the import you can just write
otherPoint.x - x
The import can be declared at any scope: usually at the top of the file, but it can go inside the method if you only need it once.
Problem 2:
math.pow works only on Double, and there's no equivalent function for all Numerics in the standard library. So convert to Double using toDouble method (you could define a generic squaring function, but not really square root).

Answer 2

First, you need an extra import to enable the convenient symbol ops on a Numeric.
After that, feed pow() a parameter type that it understands.
class Point[T: Numeric](val x: T, val y: T) {
import Numeric.Implicits._
def getDistance(otherPoint: Point[T]): Double = {
math.sqrt(math.pow((otherPoint.x - x).toDouble, 2) +
math.pow((otherPoint.y - y).toDouble, 2))
}
override def toString = "(" + x + "," + y + ")"
}