Can't use BodyInfo in Scrimmage #403

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1. Pear0 commented on Jan 16, 2017

   

   Pear0

   on Jan 16, 2017

   Contributor

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   Why do you need BodyType? Player code can only rely on battlecode/common, you shouldn't need anything in battlecode/schema.

   As far as polymorphishm goes, Robotinfo, BulletInfo, and TreeInfo all implement BodyInfo.
2. omelkonian commented on Jan 16, 2017

   

   omelkonian

   on Jan 16, 2017

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   This really needs to be solved ASAP, as it really slows down the development process.

   Polymorphism in general works as this example shows:

   def testPolymorphism[T](array: Array[T]): Boolean = true
   
   def minimalExample() = {
      val trees: Array[TreeInfo] = rc.senseNearbyTrees()
      assert(testPolymorphism(array)))
      // No exception whatsoever
   }

   But there is something wrong as this example shows:

   def minimalExample() = {
      System.out.println(
         rc.senseNearbyTrees() ++  rc.senseNearbyRobots() // InstrumentationException!
      )
      // This also throws an exception
      (rc.senseNearbyTrees(): Array[BodyInfo]) ++ (rc.senseNearbyRobots(): Array[BodyInfo])
      // The following work fine
      (rc.senseNearbyTrees(): Array[TreeInfo]) ++ (rc.senseNearbyRobots(): Array[TreeInfo])
      (rc.senseNearbyTrees(): Seq[BodyInfo]) ++ (rc.senseNearbyRobots(): Seq[BodyInfo])   
   }

   Running it results in this stack trace:

   Stack trace: 
   battlecode.instrumenter.InstrumentationException: ILLEGAL Illegal class: scala/reflect/ClassTag$
       this class cannot be referenced by player code.
           at battlecode.instrumenter.bytecode.ClassReferenceUtil.classReference(ClassReferenceUtil.java:172)
           at battlecode.instrumenter.bytecode.InstrumentingMethodVisitor.classReference(InstrumentingMethodVisitor.java:78)
           at battlecode.instrumenter.bytecode.InstrumentingMethodVisitor.visitFieldInsnNode(InstrumentingMethodVisitor.java:251)
           at battlecode.instrumenter.bytecode.InstrumentingMethodVisitor.visitMaxs(InstrumentingMethodVisitor.java:108)
           at org.objectweb.asm.ClassReader.a(Unknown Source)
           at org.objectweb.asm.ClassReader.b(Unknown Source)
           at org.objectweb.asm.ClassReader.accept(Unknown Source)
           at org.objectweb.asm.ClassReader.accept(Unknown Source)
           at battlecode.instrumenter.TeamClassLoaderFactory$Loader.instrument(TeamClassLoaderFactory.java:522)
           at battlecode.instrumenter.TeamClassLoaderFactory$Loader.loadClass(TeamClassLoaderFactory.java:443)
           at java.lang.ClassLoader.loadClass(ClassLoader.java:357)
   
3. Pear0 commented on Jan 17, 2017

   

   Pear0

   on Jan 17, 2017

   Last edited by Pear0

   Contributor

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   These are really two separate issues.

   For @revalo's issue:

   Make sure your code doesn't rely on (even import) any battlecode code that isn't in battlecode/common.

   For @omelkonian's issue:

   To fix this, the devs need to whitelist scala/reflect/ClassTag$ and possibly scala/reflect/ClassTag, but as a workaround, you can convert to any other collection and it should work just fine:

   object RobotPlayer {
     def run(rc: RobotController) {
       
       val things = rc.senseNearbyRobots().toList ++ rc.senseNearbyTrees().toList // this works
   
       println(things)
     }
   }

   Explanation:

   For historical reasons, all container types except arrays undergo type erasure. A side effect of this is that in Java, generic arrays new E[] cannot be instantiated while other containers can. Scala gets around that by using ClassTag objects which store the Class object and can use reflection to instantiate new arrays of a generic type.

   Edit: reformatted some things