RE: [boost] is_incomplete

From: Aleksey Gurtovoy (agurtovoy_at_[hidden])
Date: 2002-10-24 06:00:44

Peter Dimov wrote:
> > Hmm, actually we can do even better:
> > 
> >     #define BOOST_IS_INCOMPLETE(T) \
> >         is_incomplete< T, boost::mpl::integral_c<long,__LINE__> > \
> >     /**/
> > 
> >     template< typename T >
> >     struct something
> >         : mpl::if_c<
> >               BOOST_IS_INCOMPLETE(T)::value
> >             , something_impl1<T>
> >             , something_impl2<T>
> >             >
> >     {
> >     };
> 
> Now something<> violates ODR. ;-)

I was underslept :). Here:

    template<
          typename T
        , bool is_incomplete_ = BOOST_IS_INCOMPLETE(T)::value
        >
    struct something
        : mpl::if_c<
              is_incomplete_
            , something_impl1<T>
            , something_impl2<T>
            >
    {
    };

Actually, the macro is useless here (it doesn't really prevent
'is_incomplete' ODR violations within the same translation unit), and
frankly I don't see a way to solve this particular problem. 

So the above is useable as far as the type you are querying keeps its
"completeness property" the same within a single translation unit. Oh, well.

Aleksey