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

6 Feb 2004


      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@cc.gatech.edu)