Re: [boost] Workaround for is_better_conversion?

From: E. Gladyshev (egladysh_at_[hidden])
Date: 2003-10-31 21:15:26

--- Eric Friedman <ebf_at_[hidden]> wrote:
> To all-
> 
> Seeking to extend support of the variant< type-sequence > syntax to all 
> platforms, I've returned to the problem of simulating overload 
> resolution rules.
> 
> In this direction, I have implemented the following type trait, which 
> works as follows:
> 
>    is_better_conversion< From, To1, To2 >
>      --> true iff conversion unambiguously prefers To1 over To2
> 
> I have previously determined that is_better_conversion is sufficient to 
> implement the variant< type-sequence > syntax. Unfortunately, I cannot 
> get it to compile on MSVC6 or Borland.
> 
> If anyone could help me in this regard (see attached files), it would be 
> of great benefit to users of Boost.Variant.
> 

I did a quick check on my old MSVC6 machine

The compiler gives ICE at the line:
 typedef ::boost::mpl::bool_<
          ( sizeof( check_(from_,0) ) == sizeof( ::boost::type_traits::yes_type ) )
      > type;

If I replace it with
enum
{
  value = ( sizeof( check_(from_,0) ) == sizeof( ::boost::type_traits::yes_type ) )
};
typedef boost::mpl::bool_<value> type;

The ICE is gone but I get the 
'check_(int,int)' have different return types' error

I think the problem is that the first decration of check_()
is a template while the rest of them are not.
Somehow it messes MSVC6 up.

Eugene

__________________________________
Do you Yahoo!?
Exclusive Video Premiere - Britney Spears
http://launch.yahoo.com/promos/britneyspears/