Description Osvaldo Pinali Doederlein 2005-07-14 12:35:42 EDT

I found a new problem in support for generic types.  See this code:

interface Jukebox {
  <M extends Music, A extends Artist<M>> A getArtist (M music);
}
class JukeboxImpl implements Jukebox {
public <M extends Music,A extends Artist<M>> A getArtist (M music){return null;}
  void test () { Elvis king = getArtist(new Rock()); }
}
interface Music {}
class Rock implements Music {}
class Classic implements Music {}
interface Artist<M extends Music> {}
class Elvis implements Artist<Rock> {}
class Mozart implements Artist<Classic> {}

JDT compiler produces errors like: "The method getArtist(Rock) is ambiguous
for the type JukeboxImpl".  But JDK 1.5.0_04's javac compiles this code
normally; not only the method invocation is okay (no ambiguity), but javac
makes the assignments to 'king' and 'amadeus' without even a warning
(even if I use -Xlint:unchecked or -Xlint:all).

This behavior of javac doesn't sound very correct either, because the inferred
type of getArtist()'s return value should be "Artist<Rock>", that is not yet
assignment-compatible to Elvis, this should produce a compiler error (not just
a type-safety warning, because the incompatibility is in the erased type).

The bug in JDT is also related to inheritance.  If you remove the interface
Jukebox, this erro disappears.  There is no difference if I use interfaces,
abstract classes, or a simple base class with a concrete definition of the
method getArtist(); bug always happens if the method overrides something.