[C++-sig] Re: args patch

[Aleksey Gurtovoy]

David Abrahams wrote:
> >> I think msvc_is_incomplete<T>::value would always be true.
> >
> > Yeah. Unfortunately, that's the only way I know to implement 'has_xxx'
on
> > MSVC so that it doesn't bark on incomplete types, and there is some code
> > around which relies on it.
>
>
> It seems to me that it can't know the answer for incomplete types, and
> therefore it shouldn't produce one - it should be an error.

We don't really want that. Consider:

    #include <iosfwd>

    // ...
    typedef find_if< types, is_same<_1,std::iostream> >::type r; // error?


> How does the conforming version manage it?

SFINAE-based version just works ('has_xxx' returns 'false').

Aleksey