How do I implement a generic mathematical function in Scala
polymorphism, scala
Solution
That was one of my first questions in Stack Overflow or about Scala. The problem is that Scala maintains compatibility with Java, and that means its basic numeric types are equivalent to Java's primitives.
The problem arises in that Java primitives are not classes, and, therefore, do not have a class hierarchy which would allow a "numeric" supertype.
To put it more plainly, Java, and, therefore, Scala, does not see any common grounds between a `Double`'s `+` and a an `Int`'s `+`.
The way Scala finally got around this restriction was by using `Numeric`, and its subclasses `Fractional` and `Integral`, in the so-called typeclass pattern. Basically, you use it like this:
def square[T](x: T)(implicit num: Numeric[T]): T = {
import num._
x * x
}
Or, if you do not need any of the numeric operations but the methods you call do, you can use the context bound syntax for type declaration:
def numberAndSquare[T : Numeric](x: T) = x -> square(x)
For more information, see the answers in my own question.
Problem
I'm just getting started with Scala and something which I think should be easy is hard to figure out. I am trying to implement the following function: `def square(x:Int):Int = { x * x }` This works just fine, but if I want to try to make this function work for any kind of number I would like to be able to do the following: `def square[T <: Number](x : T):T = { x * x }` This complains and says: error: value * is not a member of type parameter T Do I need to implement a trait for this?