I have the following (simplified) code:
case class Value[T](value: T)
trait Absable[In,Out] {
def absoluteValue(in: In): Out
}
implicit class AbsValue[In, Out](in: Value[In]) {
def abs()(implicit ev: Absable[In, Out]): Value[Out] = Value(ev.absoluteValue(in.value))
}
implicit def AbsNumeric[A : Numeric] = new Absable[A, A] {
def absoluteValue(in: A) = implicitly[Numeric[A]].abs(in)
}
Now I want to use the abs
function on a Value
:
scala> Value(-3).abs()
res3: Value[Int] = Value(3)
scala> Value(-3).abs
<console>:14: error: could not find implicit value for parameter ev: Absable[Int,Nothing]
Value(-3).abs
^
I added an empty argument list in front of the implicit arguments to give callers more flexibility, but now when I omit the empty list at the call site the compiler can't find the implicit... So now instead of more flexibility callers get confusing compile errors.
I don't understand how leaving off the argument list can affect the type inference or implicit resolution.
I am using scala 2.11.6