| [#501] | project: nsc | priority: low | category: bug | |
|---|---|---|---|---|
| submitter | assigned to | status | date submitted | |
| Philippe | Martin | fixed | 2005-11-28 13:39:45.0 | |
| subject | Scala is unsound | |||
| code |
object Magic {
class O[X,Y] {
abstract class I { type T >: X <: Y; }
val i: I = null;
def magic(v: i.T): i.T = v;
}
def magic[X,Y](v: X): Y = {
val o: O[X,Y] = new O();
o.magic(v);
}
}
object Test {
def main(args: Array[String]): Unit = {
val i: Int = Magic.magic("42");
System.out.println(i);
}
}
|
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| what happened | Exception in thread "main" java.lang.ClassCastException at Test$.main(test.scala:16) at Test.main(test.scala) |
|||
| what expected | The method Magic.magic converts any value of any type X to any other type Y without using any cast. The implementation relies on the fact that the method Magic.O.magic raises no NPE although its argument type and return type extract the type T from the value i which is null.
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| [back to overview] | ||||
| Philippe edited on 2005-11-28 14:21:09.0 |
| Changed project to "nsc". |
| Martin edited on 2006-02-02 15:28:08.0 |
| I am not claiming (yet) that scala is sound but the particular two problems that Philippe has discovered are fixed. Bug 501 is fixed because lower bounds must now statically conform to upper bounds. Bug 500 is fixed because outer references are now checked to be non-null. |