Acces to private field from nested class when the type of reference is a generic type variable with upper bound of outer class

[Peter Levart]

On Friday, October 07, 2011 11:15:13 PM maurizio cimadamore wrote:
> An intersection type A1, A2 ... An is defined as the most general type 
> that is a subtype of both A1, A2 ... An.
> Since it is a subtype of all its components, it follows it should 
> contain the members of the 'union' of the components. However, since 
> it's a subtype, private members in supertypes are not inherithed.
> 
> Maurizio

Quite true. And that's understandable for private field access.

And now for some puzzlers. Let's take that definition and a look at the following program:


package test;

public class Test
{
    public static class A
    {
        public int field = 1;
    }

    public static class B extends A
    {
        public int field = 2;
    }

    public static class FieldGetter<T extends A>
    {
        public int getField(T obj)
        {
            return obj.field;
        }
    }

    public static void main(String[] args)
    {
        A a = new A();
        B b = new B();

        FieldGetter<A> aFieldGetter = new FieldGetter<A>();
        FieldGetter<B> bFieldGetter = new FieldGetter<B>();

        System.out.println(a.field); // 1
        System.out.println(b.field); // 2

        System.out.println(aFieldGetter.getField(a)); // 1
        System.out.println(aFieldGetter.getField(b)); // 1

        System.out.println(bFieldGetter.getField(b)); // 1 !!!
    }
}


... in FieldGetter the T is the most general type that is a subtype of A and any subtypes of A 
(which includes B). Now A.field is inherited by any subtypes of A, but it can also be hidden by 
fields of the same name in any of the subtypes of A (as is in the example by B.field).

The question is: How can compiler decide which field to access in T.getField method?

Would it be right to disallow "any" field access via the type-variable typed variables?

The joys of erasure!

Peter