Re: [boost] ODR violations in typeof, was: boost::typeof, MSVC7.1 & 8.0, and precompiled heade

From: Peder Holt (peder.holt_at_[hidden])
Date: 2006-06-09 01:38:42

On 6/9/06, Arkadiy Vertleyb <vertleyb_at_[hidden]> wrote:
> "Peder Holt" <peder.holt_at_[hidden]> wrote
>
> > I tried compiling the test battery on VC8 with precompiled headers
> > enabled (\Yc with test.hpp as the precompiled header) and encountered
> > similar problems. Eliminating the anonymous namespaces solves the
> > problem, and doesn't introduce any obvious new problems. Is there more
> > than a theoretical reason for the anonymous namespaces in the first
> > place? Is there any observed cases where not having anonymous
> > namespaces causes corruption to typeof?
>
> There are no observed cases, AFAIK.
>
> However, there is also not a lot of experience.  ODR is definitely violated,
> one way or another.  Compilers don't seem to complain about our ODR test,
> but this test is designed for anonymous namespaces.  I can also imagine that
> some compilers may report ODR violation only in certain context.  And we
> never know what new [versions of] compilers will do.
>
> It's easy to make the usage of anonymous namespace configurable by
> introducing something like BOOST_TYPEOF_SUPRESS_UNNAMED_NAMESPACE.  I would
> also add another ODR test, targeted to this mode.
>
> Having two possibilities may give a better chance of avoiding potential
> issues with ODR.  And having the mode without unnamed namespace would also
> allow the user to completely avoid ODR by always registering in the same
> order (having system-wide registration header), although at the expence of
> dependency bottleneck.
>
> Does this make sence?

Makes sense. A good test then would be:
File 1
#include <boost/typeof.hpp>
#include <type_registration1.hpp>
#include <type_registration2.hpp>

Use TYPEOF on types registered in type_registrationx.hpp

File 2
#include <boost/typeof.hpp>
#include <type_registration2.hpp>
#include <type_registration1.hpp>

Use TYPEOF on types registered in type_registrationx.hpp

We should probably disable anonymous namespaces by default when using
precompiled headers. Is there a #define to check if precompiled
headers is used?

Regards, Peder

>
> Regards,
> Arkadiy
>
>
>
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