Defining generic function that uses arithmetic operation

Question

Hi I am trying to define a generic function isNonNeg that makes use of an arithmetic operator as follows:

scala> def isNonNeg[A](a:A): Boolean = { if (a >= 0.0) true else false}

However this produces the following error:

<console>:13: error: value >= is not a member of type parameter A
   def isNonNeg[A](a:A): Boolean = { if (a >= 0.0) true else false}
                                           ^

I'm assuming that the problem is because type A is unknown. Is there a way of specifying that A should be a numeric type hence >= is a valid operator. Would some sort of type class or implicit parameter offer a solution ?

Alvaro Carrasco · Accepted Answer · 2016-05-27 22:48:06Z

2

You can use the Numeric typeclass: http://www.scala-lang.org/api/2.11.8/#scala.math.Numeric

def isNonNeg [A](a: A)(implicit ev: Numeric[A]) = ev.gteq(a, ev.zero)

If you want to use the operator, you can import Ordering.Implicits:

import Ordering.Implicits._
def isNonNeg [A](a: A)(implicit ev: Numeric[A]) = a >= ev.zero

edited May 27, 2016 at 22:48

answered May 27, 2016 at 22:42

Alvaro Carrasco

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