Although the following technique for simulating variant type parameters won't
work in general because of the rule "It is an error if most specific parameter
types do not exist or are not unique", the following program violates none of
the constraints in the JSR14 specification, yet the prototype compiler will not
compile it. I don't know if this is a bug in the specification or the
prototype.





import java.util.ArrayList;
import java.util.Iterator;
import java.util.List;

interface UnaryFunction<A,X> { X apply(A a); }

class IdentityFunction<A>
    implements UnaryFunction<A,A>
{
    public A apply(A a) { return a; }
}

class Util {
    private Util() {}

    static
<X,Y extends X,A,B extends A> List<X> map(UnaryFunction<A,Y> f,
List<B> list)
    {
ArrayList<X> l = new ArrayList<X>(list.size());
Iterator<B> i = list.iterator();
while (i.hasNext()) {
B b = i.next();
Y y = f.apply(b);
l.add(y);
}
return l;
    }

    static List<Object> ol2ol(List<Object> ol) {
List<Object> ol2 = map(new IdentityFunction<Object>(), ol);
return ol2;
    }
}