Re: [boost] variant - is there an easy way to tell if an object is a variant at compile time?

From: Brian McNamara (lorgon_at_[hidden])
Date: 2004-02-05 19:46:09

On Thu, Feb 05, 2004 at 06:28:27PM -0600, Brock Peabody wrote:
> Is there an easy way to write:
> 
>    template <typename T> struct is_variant {
> 
>       typedef ??? type;
>    };
> 
> So far the best I can come up with is:
> 
> 1) T has a member type "types" and 
> 2) T is convertible to make_variant_over<T::types>::type and
> 3) make_variant_over<T::types>::type is convertible to T
> 
> Does anyone have a better idea?

Perhaps I'm missing something, but why not just something like

   template <typename T> struct is_variant {
      typedef false_ type;
   };
   template <typename T1, typename T2, ... /*however many*/> 
   struct is_variant<variant<T1,T2,...> > {
      typedef true_ type;
   };

?

-- 
-Brian McNamara (lorgon_at_[hidden])