Re: Visibility and C++ Classes/Templates

[Ian Lance Taylor <iant at google dot com>]

Mark Mitchell <mark@codesourcery.com> writes:

> Jason Merrill wrote:
> > Now, templates:
> > 
> >   template<class T> __attribute((visibility ("hidden")) T f(T);
> >   #pragma GCC visibility push(default)
> >   extern template int f(int);
> >   #pragma GCC visibility pop
> > 
> > This could really go either way.  It could be considered similar to the
> > above case in that f<int> is in a way "part" of f<T>, but there isn't
> > the same scoping relationship.  Also, there isn't the
> > declaration/definition problem, as the extern template directive is the
> > first declaration of the instantiation.  In this case I am inclined to
> > respect the #pragma rather than the attribute on the template.
> 
> I'd tend to say that the attribute wins, and that if you want to specify
> the visibility on the template instantiation, you must use the attribute
> on the instantiation, as you suggest:

Don't you still have to deal with this case?

#pragma GCC visibility push(hidden)
template<class T> T f(T);
#pragma GCC visibility pop
...
#pragma GCC visibility push(default)
extern template int f(int);
#pragma GCC visibility pop

Personally I wouldn't mind saying that the attribute always beats the
pragma, but it seems to me that there is still the potential for
ambiguity.

Ian