Re: [Boost-users] [tuple] weird compile error with VC-8_0

From: Andy Little (andy_at_[hidden])
Date: 2006-09-07 06:49:56

<imre_at_[hidden]> wrote in message
news:20060907060211.DFA9D1054D4_at_wowbagger.osl.iu.edu...
> Hi,
>
> I am getting this error message, when using boost::tuple:
>
> include\boost\tuple\detail\tuple_basic.hpp(373) : error C2039: 'tail' : is
> not a member of 'boost::tuples::cons<HT,TT>'
> 1>        with
> 1>        [
> 1>            HT=UTX::DB::nulled_type<unsigned char>,
> 1>            TT=boost::tuples::null_type
> 1>        ]
>
> The referred line is the templated constructor of the non-specialised struct
> cons:
>
> template <class HT2, class TT2>
> cons( const cons<HT2, TT2>& u ) : head(u.head), tail(u.tail) {}
>
> So it seems that somehow the non-specialised method is called for the
> specialised template instantiation.  Has anybody seen something like this?

Yes.

> Is there a way to circumvent it?

With me it happened because the compiler was instantiating (unintended) stuff
where the tuple was too short.

You could try using enable_if on a very general signature instead of
specialisation to prevent the compiler 'looking into' stuff. IOW

Before:

template <int N> struct my;

template <> struct my<1>{...};

After:

template <int N, typename Enable = void> struct my; // <--- for boost::enable_if

template <int N>
struct my <N, typename boost::enable_if_c<(N==1) >::type> {...};

HTH

regards
Andy Little