[Bug c++/12429] New: Template class Foo<X> cannot access private members of Foo<Y>

[Bug c++/12429] New: Template class Foo<X> cannot access private members of Foo<Y>

[sean dot gies at discreet dot com]

PLEASE REPLY TO gcc-bugzilla@gcc.gnu.org ONLY, *NOT* gcc-bugs@gcc.gnu.org.

http://gcc.gnu.org/bugzilla/show_bug.cgi?id=12429

           Summary: Template class Foo<X> cannot access private members of
                    Foo<Y>
           Product: gcc
           Version: 3.3
            Status: UNCONFIRMED
          Severity: normal
          Priority: P2
         Component: c++
        AssignedTo: unassigned at gcc dot gnu dot org
        ReportedBy: sean dot gies at discreet dot com
                CC: gcc-bugs at gcc dot gnu dot org

Member functions of template classes cannot access protected or private members of a different 
specialization of itself, nor can a friendship be declared to allow the access.

The only workaround involves hacking the public interface of the template class.

For example, private member function Bar(int) of class Foo<float> cannot call Bar(int) of class 
Foo<int>:

template <class T> class Foo {
        template <class F> friend class Foo<F>; // This attempted work-around also fails
        void Bar(int x=0) {if (x<4) Foo<int>().Bar(x+1);}
public:
        void Test() {Bar();}
};
int main(int argc, char** argv) {
        Foo<float>().Test();
}

[Bug c++/12429] Template class Foo<X> cannot access private members of Foo<Y>

[pinskia at gcc dot gnu dot org]

PLEASE REPLY TO gcc-bugzilla@gcc.gnu.org ONLY, *NOT* gcc-bugs@gcc.gnu.org.

http://gcc.gnu.org/bugzilla/show_bug.cgi?id=12429



------- Additional Comments From pinskia at gcc dot gnu dot org  2003-09-27 01:54 -------
I think the code is invalid as different specialization are really different classes.
The way to fix this is make Foo<int> a friend.

[Bug c++/12429] Template class Foo<X> cannot access private members of Foo<Y>

[pinskia at gcc dot gnu dot org]

PLEASE REPLY TO gcc-bugzilla@gcc.gnu.org ONLY, *NOT* gcc-bugs@gcc.gnu.org.

http://gcc.gnu.org/bugzilla/show_bug.cgi?id=12429


pinskia at gcc dot gnu dot org changed:

           What    |Removed                     |Added
----------------------------------------------------------------------------
             Status|UNCONFIRMED                 |RESOLVED
         Resolution|                            |INVALID


------- Additional Comments From pinskia at gcc dot gnu dot org  2003-09-27 05:49 -------
Here is how to fix you code (yes I was right about "different specialization are really 
different classes", the problem was that you were trying make friends with specializations 
which is wrong):
template <class T> class Foo {
        template <class Y> friend class Foo;
        void Bar(int x=0) {if (x<4) Foo<int>().Bar(x+1);}
public:
        void Test() {Bar();}
};
int main(int argc, char** argv) {
        Foo<float>().Test();
}

[Bug c++/12429] Template class Foo<X> cannot access private members of Foo<Y>

[sean dot gies at discreet dot com]

PLEASE REPLY TO gcc-bugzilla@gcc.gnu.org ONLY, *NOT* gcc-bugs@gcc.gnu.org.

http://gcc.gnu.org/bugzilla/show_bug.cgi?id=12429



------- Additional Comments From sean dot gies at discreet dot com  2003-09-29 19:45 -------
Subject: Re:  Template class Foo<X> cannot access private members of Foo<Y>

Thank you for the fix.  Just when I thought I finally understood  
templates. :)

-Sean

On Friday, September 26, 2003, at 10:49  PM, pinskia at gcc dot gnu dot  
org wrote:

> PLEASE REPLY TO gcc-bugzilla@gcc.gnu.org ONLY, *NOT*  
> gcc-bugs@gcc.gnu.org.
>
> http://gcc.gnu.org/bugzilla/show_bug.cgi?id=12429
>
>
> pinskia at gcc dot gnu dot org changed:
>
>            What    |Removed                     |Added
> ----------------------------------------------------------------------- 
> -----
>              Status|UNCONFIRMED                 |RESOLVED
>          Resolution|                            |INVALID
>
>
> ------- Additional Comments From pinskia at gcc dot gnu dot org   
> 2003-09-27 05:49 -------
> Here is how to fix you code (yes I was right about "different  
> specialization are really
> different classes", the problem was that you were trying make friends  
> with specializations
> which is wrong):
> template <class T> class Foo {
>         template <class Y> friend class Foo;
>         void Bar(int x=0) {if (x<4) Foo<int>().Bar(x+1);}
> public:
>         void Test() {Bar();}
> };
> int main(int argc, char** argv) {
>         Foo<float>().Test();
> }
>
>
>
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