[GiNaC-list] Problem using a user-defined class on Mac OS X.

[Sheplyakov Alexei]

Hello,

On Wed, Apr 04, 2007 at 09:34:24PM -0400, David Fang wrote:
> > C++ standard allows this (see e.g. 14.7.3).
> >
> > So, this is OK:
> >
> > template<typename T> class foo {
> > 	static T data;
> > };
> >
> > template<typename T> class foo<T*> {
> > 	static void* data;
> > };
> >
> > template<typename T> T foo<T>::data = T(1);
> >
> > template<typename T> void* foo<T*>::data = 0;
> 
> Hi,
> 	This alone doesn't exhibit the issue in the original example.
> What you've written above is just a plain partial specialization, no
> violation at all.

IMHO the patch in question is just explicit specialization, no violations
either. 

> Now, suppose that the last definition above
> (foo<T*>::data) was replaced in a *different* translation unit with:
> 
> template <> void* foo<void*>::data = &something_else;
>
> which is similar to the original code in this thread.  The instantiation
> of foo<void*>::data can now be different-valued.  (Is this analogous to
> the GiNaC source or proposed patch in question?)

That's a different story. What we have is _equivalent_ explicit 
specialization, like

template<typename T> class bar {
	static void* data;
};

template<typename T> bar<T>::data = 0;

struct baz { };

// in a different translation unit:

template<> bar<baz>::data = 0;

So there should be no any difference. But... Apparently compiler generates
different code:

// With explicit specialization
$ nm -B -C build/ginac/ginac/.libs/libginac.so  | grep -e '::first'
0032bc8c B GiNaC::class_info<GiNaC::print_context_options>::first
0032bc84 B GiNaC::class_info<GiNaC::registered_class_options>::first

// _Without_ explicit specialization
nm -B -C build/ginac/ginac/.libs/libginac.so  | grep -e '::first'
002611d0 V GiNaC::class_info<GiNaC::print_context_options>::first
00261168 V GiNaC::class_info<GiNaC::registered_class_options>::first

I need to re-read the standard to understand what's going on...

Best regards,
 Alexei

-- 
All science is either physics or stamp collecting.

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