Can't get inherited vals with Scala reflection - scala

Question

I'm using Scala 2.10.1 and I'm trying the define a method which will retrieve all the vals (including the inherited ones) from an object.
I have the following:
import scala.reflect.runtime.{universe => ru}
object Reflection {
val mirror = ru.runtimeMirror(this.getClass.getClassLoader)
def findVals(x: Any): Iterable[String] = {
val theType = mirror.classSymbol(x.getClass).toType
theType.members.collect({case x if x.isTerm => x.asTerm}).filter(_.isVal).map(_.name.toString)
}
}
I am testing on these two classes:
class Base {
val x = 10
}
class Child extends Base {
val y = 20
}
When calling the following code:
val x = new Child
val vs = Reflection.findVals(x)
println(vs)
The result is List(y)
For some reason, the isVal method returns false for the term corresponding to the x field from the Base class.
Can someone tell me what's the problem here? Am I doing something wrong?

Answer 1

Per Why don't Scala case class fields reflect as public? you should use isAccessor instead of isVal.
I'm actually using isGetter and setter to properly filter vars per your comment:
def findVals(x: Any): Iterable[String] = {
val theType = mirror.classSymbol(x.getClass).toType
val xtm = theType.members.collect({case x if x.isTerm => x.asTerm})
xtm.filter(m => m.isGetter && !xtm.exists(m.setter == _)).map(_.name.toString)
}
Results:
scala> class Base {
| var x = 10
| val xx = 2
| }
defined class Base
scala> class Child extends Base {
| val y = 3
| }
defined class Child
scala> val x = new Child
x: Child = Child#1c0026e
scala> val vs = Reflection.findVals(x)
vs: Iterable[String] = List(y, xx)
scala> println(vs)
List(y, xx)

Answer 2

Using SMirror:
scala> implicit val mirror = scala.reflect.runtime.currentMirror
mirror: reflect.runtime.universe.Mirror = JavaMirror with scala.tool…
scala> import net.fwbrasil.smirror._
import net.fwbrasil.smirror._
scala> class Base {
val x = 10
}
defined class Base
scala> class Child extends Base {
val y = 20
}
defined class Child
scala> val x = new Child
x: Child = Child#448593d0
scala> x.reflect.vals
res5: List[net.fwbrasil.smirror.SInstanceVal[Child]] = List(val x: scala.Int (bound to Child#448593d0), val y: scala.Int (bound to Child#448593d0))
scala> x.reflect.vals.head.get
res7: Any = 10

Answer 3

So, this is terribly inelegant, but it seems to work:
import scala.reflect.runtime.{universe => ru}
object Reflection {
val mirror = ru.runtimeMirror(this.getClass.getClassLoader)
val ObjectClass = classOf[java.lang.Object];
def findVals(x: Any) : Iterable[String] = findVals( x.getClass, List.empty );
def findVals(clz: Class[_], accum : Iterable[String]): Iterable[String] = {
clz match {
case ObjectClass => accum;
case _ => {
val theType = mirror.classSymbol(clz).toType
val newVals = theType.members.collect({case x if x.isTerm => x.asTerm}).filter(_.isVal).map(_.name.toString)
findVals( clz.getSuperclass, accum ++ newVals )
}
}
}
}
Then...
scala> class Base {
| val x = 10
| var z = 20
| }
defined class Base
scala> class Child extends Base {
| val y = 20
| var a = 9
| }
defined class Child
scala> val x = new Child
x: Child = Child#3093266d
scala> val vs = Reflection.findVals(x)
vs: Iterable[String] = List("y ", "x ")
scala> println(vs)
List(y , x )
It seems that, at least for now, Scala reflection looks at the Java field to determine the presence of a val, so I guess you just have to climb the class hierarchy... I'm guessing it looks for the presence of a setter to distinguish val from var. Again, not so lovely, but functional.