While investigating issue DAFFODIL-2146, I discovered that dstate.currentValue
was taking on the value of "One(0)".
My first instinct is to attribute the to a bug in my enumeration support code
(which it probably is), however my second instinct is to note that
dstate.currentValue is declared to be of type AnyRef, while One(0) is of type
Maybe, so the above situation should not be possible.
I was able to reproduce the issue in a small test program (using Daffodil as a
dependency):
val x1: Maybe[JLong] = One(JLong.valueOf(0))
val x : Any = x1
val y: AnyRef = Numbers.asAnyRef(x)
println(x1.isInstanceOf[AnyRef])
println(x.isInstanceOf[AnyRef])
println(y)
I would expect the above program to output (not sure what I expect on the third
line):
false
false
????
However, it actually outputs:
true
true
One(0)
Helpfully, Eclipse provides a warning on the first println that the expression
can never be true.
For reference, Numbers.asAnyRef is defined as:
def asAnyRef(n: Any): AnyRef = {
n match {
// case bi: BigInt => bi.bigInteger
// case bd: BigDecimal => bd.bigDecimal
case ar: AnyRef => ar
case b: Boolean => JBoolean.valueOf(b)
case _ => asNumber(n)
}
}
and I observe the same behaviour if I replace that call with a local version of
the function:
def asAnyRef(n: Any): AnyRef = {
n match {
case ar: AnyRef => ar
}
}
What appears to be happening is that Maybe is being recognized as an AnyRef by
the pattern match, thereby allowing for a Maybe -> AnyRef cast which should not
be possible.
Based on this, I tested the behavour of Numbers.asAnyRef on scala.Int value and
found (by println debugging) that such a case is also going the the ar:AnyRef
code path.
I suspect that the asAnyRef function is always a no-op at runtime, and the only
reason our works normally is that scala will automagically cast between boxed
and unboxed versions of the built-in anyVal types.
Assuming my analysis is correct, asAnyRef is really unsafeCoerceToAnyRef. As
such, I would suggest that we remove the function and explicitly box values
where Scala fails to do so automatically.
Thoughts?
Brandon T. Sloane
Associate, Services
[email protected] | tresys.com
