CODEWITHSUNDEEP
scalareflectionscalatestmirror
Abhijit Sarkar
Abhijit Sarkar

Reputation: 24593

Scala: Ordering[Int].lt invocation fails for reflective method call

I'm playing with Scala reflection and ScalaTest. I've a method defined as follows in an object Ch2: def isSorted[A](as: Array[A], ordered: (A, A) => Boolean): Boolean

The following test fails as described in the comment:

"Method isSorted" should "return true for a sorted array" in {
    val methods =
      Table(
        ("method"),
        ("isSorted")
      )

    val m = ru.runtimeMirror(getClass.getClassLoader)
    val mod = ru.typeOf[Ch2.type].termSymbol.asModule
    val mm = m.reflectModule(mod)
    val obj = mm.instance
    val im = m.reflect(obj)

    forAll(methods) { (m: String) =>
      val isSortedMethod = ru.typeOf[Ch2.type].decl(ru.TermName(m)).asMethod
      val isSorted = im.reflectMethod(isSortedMethod)

      // Fails at runtime with 'missing parameter type for expanded function'
      isSorted(Array(1, 2, 3, 4), Ordering[Int].lt(_, _))
    }
}

Of course, I could replace Ordering[Int].lt with (x: Int, y: Int) => x < y and it'd work but I'd rather use what's already provided instead of rolling my own.

Upvotes: 0

Views: 48

Answers (1)

Archeg
Archeg

Reputation: 8462

The compiler cannot infer type A in your call. Try to make the call without reflection.

You should specify type during call like 

isSorted(Array(1, 2, 3, 4), (x: Int, y: Int) => Ordering[Int].lt(x, y))

Upvotes: 1

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