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reflection behaves badly with respect to value class fields #7328

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scabug opened this issue Apr 4, 2013 · 7 comments
Closed

reflection behaves badly with respect to value class fields #7328

scabug opened this issue Apr 4, 2013 · 7 comments

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@scabug
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@scabug scabug commented Apr 4, 2013

Reflection understands correctly the type of value-class fields, but the instance mirrors return values of the wrong type when accessing these fields:

import scala.reflect.runtime._

case class Foo(x: Int) extends AnyVal
case class Bar(foo: Foo)

object Test {
  def main(args: Array[String]) {
    val fooTerm = universe.typeOf[Bar].declaration(universe.newTermName("foo")).asMethod
    val fooType = fooTerm.returnType // correctly gives typeOf[Foo]
    println(fooType) // Foo

    val bar = Bar(Foo(3))
    println(bar.foo) // Foo(3)

    val im = currentMirror.reflect(bar)

    val obj1 = im.reflectField(fooTerm).get // incorrectly gives java.lang.Integer(3) not Foo(3)
    println(obj1) // 3

    val obj2 = im.reflectMethod(fooTerm)() // ditto
    println(obj2) // 3
  }
}
@scabug
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@scabug scabug commented Apr 4, 2013

Imported From: https://issues.scala-lang.org/browse/SI-7328?orig=1
Reporter: Jeff Olson (jdolson)
Affected Versions: 2.10.1

@scabug
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@scabug scabug commented Apr 9, 2013

@xeno-by said:
Workaround, courtesy of Jeff Olson:

  def getFieldValue(im: InstanceMirror, term: MethodSymbol): Any = {
    val rawValue = im.reflectMethod(term)()
    val tpe = term.returnType
    val symbol = tpe.typeSymbol.asClass
    if (symbol.isDerivedValueClass) {
      val ctor = tpe.declaration(nme.CONSTRUCTOR).asMethod
      val ctorMirror = mirror.reflectClass(symbol).reflectConstructor(ctor)
      ctorMirror(rawValue)
    }
    else rawValue
  }

@scabug
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@scabug scabug commented Apr 11, 2013

Jeff Olson (jdolson) said:
This may be obvious, but setters are broken too:

import scala.reflect.runtime.universe._

case class Foo(n: Int) extends AnyVal
class Bar(var foo: Foo)

object Test {
  def main(args: Array[String]) {
    val bar = new Bar(Foo(3))

    val mirror = runtimeMirror(getClass.getClassLoader)
    val im = mirror.reflect(bar)
    val fooTerm = typeOf[Bar].declaration(newTermName("foo")).asTerm
    val fooField = im.reflectField(fooTerm)
    fooField.set(Foo(5)) // java.lang.IllegalArgumentException: Can not set int field Bar.foo to Foo
    fooField.set(5) // this works but probably shouldn't
    println(bar.foo)
  }
}

@scabug
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@scabug scabug commented Apr 11, 2013

Jeff Olson (jdolson) said:
And constructors as well. However, in this case, there doesn't seem to be a workaround (at least that I've found so far):

import scala.reflect.runtime.universe._

case class Foo(n: Int) extends AnyVal
case class Bar(foo: Foo)

object Test { 
  def main(args: Array[String]) {
    val mirror = runtimeMirror(getClass.getClassLoader)
    val cm = mirror.reflectClass(typeOf[Bar].typeSymbol.asClass)
    val ctor = typeOf[Bar].declaration(nme.CONSTRUCTOR).asMethod
    val ctorm = cm.reflectConstructor(ctor)
    ctorm(Foo(3)) // java.lang.NoClassDefFoundError: no Java class corresponding to ErasedValueType(Foo) found
    ctorm(3)      // java.lang.NoClassDefFoundError: no Java class corresponding to ErasedValueType(Foo) found
  }
}

@scabug
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@scabug scabug commented May 20, 2013

@JamesIry said:
2.10.2 is about to be cut. Kicking down the road and un-assigning to foster work stealing.

@scabug
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@scabug scabug commented Jan 24, 2014

@xeno-by said:
The thing with constructors is #6411, which has just been fixed in a pull request.

@scabug
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@scabug scabug commented Jan 24, 2014

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