Hiding inherited protected member

[Fabio Cannizzo]

Is there a way to hide an inherited protected member so that it is no longer
accessible nor visible from the inherited classes?

The code below makes c1.foo() no longer accessible, but c2.foo is visible to
c3! If instead I make c2.foo private, then c3 will access directly c1.foo

Thanks, Fabio

class c1 {
protected void foo() { MessageBox.Show( "foo: c1" ); }
}

class c2 : c1 {
protected new void foo() { /*stub function */ }
}

class c3 : c2 {
public void zoo() { foo(); }
}

[Jon Skeet [C# MVP]]

Fabio Cannizzo <fc*****************@london.edu> wrote:

Is there a way to hide an inherited protected member so that it is no longer
accessible nor visible from the inherited classes?

No. If a member shouldn't be visible from inherited classes, it
shouldn't be protected.

--
Jon Skeet - <sk***@pobox.com>
http://www.pobox.com/~skeet
If replying to the group, please do not mail me too

[Fabio Cannizzo]

I guess that means that if I specialise a class in the hierarchy so that
cartain functionality becomes imposed, and no longer user choice, that is
not possible.
Bless the old C++, which allowed for private inheritance! While I admit it
is exceptional for GUIs, it is so limited for other things. Hope the 2.0
will be better.

Thank you for your reply.

Fabio
"Jon Skeet [C# MVP]" <sk***@pobox.com> wrote in message
news:MP************************@msnews.microsoft.c om...

Fabio Cannizzo <fc*****************@london.edu> wrote:

Is there a way to hide an inherited protected member so that it is no
longer
accessible nor visible from the inherited classes?

No. If a member shouldn't be visible from inherited classes, it
shouldn't be protected.

--
Jon Skeet - <sk***@pobox.com>
http://www.pobox.com/~skeet
If replying to the group, please do not mail me too

[Bruce Wood]

The problem goes something like this:

If C# were to allow you to override members and make them private in
derived classes, then all the caller has to do is cast the object to
its base class in order to get at the member again. The compiler, not
knowing that this variable holds an upcast instance of a derived class
in which the method or property is private, will allow access to the
member via the vtable, even though it is marked "private" in the
derived class.

I suppose that the run time could throw an exception indicating that
you're trying to access an overridden private member, but then you're
incurring the overhead of run-time access checking.

The best you can do is, as you pointed out, declare the method or
property as "private new". Are you sure that if you declare it "private
new", the derived class (c3) can still get at "foo"? (Of course, it can
always upcast and get at it, but I mean without doing that trick.)

[Fabio Cannizzo]

Hi Bruce.

Thaks for your reply.

I have tried the downcasting trick, and that, at least, seems to be
protected. When in c3 I upcast to c1, then c3 is treated just as another
class, and it does not have rights to access private or protected members of
c1.

Fabio

"Bruce Wood" <br*******@canada.com> wrote in message
news:11*********************@g49g2000cwa.googlegro ups.com...

The problem goes something like this:

If C# were to allow you to override members and make them private in
derived classes, then all the caller has to do is cast the object to
its base class in order to get at the member again. The compiler, not
knowing that this variable holds an upcast instance of a derived class
in which the method or property is private, will allow access to the
member via the vtable, even though it is marked "private" in the
derived class.

I suppose that the run time could throw an exception indicating that
you're trying to access an overridden private member, but then you're
incurring the overhead of run-time access checking.

The best you can do is, as you pointed out, declare the method or
property as "private new". Are you sure that if you declare it "private
new", the derived class (c3) can still get at "foo"? (Of course, it can
always upcast and get at it, but I mean without doing that trick.)