possible bug with pointer to template member function

[rodolfo at rodsoft dot org]

Hi, I've come with a problem with g++ 4.1.1 and people at gcc-help said
they think it's a bug, so I'll forward my original email to this list.

Regards,
    Rodolfo Lima

----- Forwarded message from Rodolfo Schulz de Lima <rodolfo@rodsoft.org> -----

> Date: Fri, 13 Oct 2006 14:05:27 -0300
> From: Rodolfo Schulz de Lima <rodolfo@rodsoft.org>
> To: gcc-help@gcc.gnu.org
> Subject: pointer to template member function
> User-Agent: Mutt/1.5.11
> 
> Hi, I´ve come across the following code, which g++ refuses to compile:
> 
> // ---
> struct A
> {
>     void a() {}
> };
> 
> struct B : A
> {
>     template <class T> void b() {}
> };
> 
> typedef void (A::* ptr)();
> 
> int main()
> {
>     ptr x = &A::a, // 
> 	y = static_cast<ptr>(&B::b<int>); // g++ chokes here
> }
> // ---
> 
> G++ says that 
> 
> error: invalid static_cast from type 
> 	'<unresolved overloaded function type>' to type 'void (A::*)()'
> 
> But if I make void b() a non-template class and modify the cast to
> static_cast<ptr>(&B::b) it compiles fine. If this is valid, why the
> template case isn't?
> 
> I'd really say that either casts shouldn't be valid, because in the
> non-template case, I could do:
> 
>   A a;
>   (a.*x)(); // fine, x points to a member of A, and we are using it with
> 	    // an instance of A.
> 
>   (a.*y)(); // this will have unpredictable results if B::b relies on
> 	    // a B's attribute, because we're using B::* with an A
> 	    // instance. static_casts should be 'safe', aren't they?
> 
> Fortunately, both cases fail when using the default cast without
> static_cast. In the template case, compilation fails with:
> 
> error: no matches converting function 'b' to type 'void (struct A::*)()'
> error: candidates are: template<class T> void B::b()
> 
> And in the non template case, compilation fails with:
> 
> error: cannot convert 'void (B::*)()' to 'void (A::*)()' in
> initialization
> 
> 
> Thanks,
>     Rodolfo Lima.

----- End forwarded message -----