Geoffrey Keating wrote:
[#pragma visibility affecting explicit instantiations]
A consequence of this is that if a user instantiates a template that
they don't 'own' (that is, a template from a different module), they
must make sure that no #pragma is in effect, because the other module
may have a specific idea about what visibility should be used.
Can you give an example? You can also get different visibility
implicitly, if a template argument has more restricted visibility than
the template; the instantiation gets the more restricted one.
I'm not sure how exactly they can do this. Is there a visibility
pragma for "no setting"?
#pragma GCC visibility pop
It seems like this would be a common enough mistake that there should
be a way to get a warning about it.
I think it would be intentional more often than it would be a mistake.
In the traditional declaration/definition model, if you try to change
the linkage of something you get an error...
Yes. If you try to change the visibility of something you also get an
error. But an instantiation need not have the same visibility as its
template.
For instance, code coming from VC++ will tend to default to hidden
visibility, but make the interfaces default visibility. If a particular
instantiation of a template is part of the interface of a non-template
class, it must also get default visibility.
Jason
