Brian McNamara wrote:
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; };
?
Precisely, template <typename T> struct is_variant : mpl::false_ {}; template <BOOST_VARIANT_ENUM_PARAMS(typename T)> struct is_variant< variant<BOOST_VARIANT_ENUM_PARAMS(T)> > : mpl::true_ {}; should do the trick. If this is deemed useful, I can include it in the next release. For now, BOOST_VARIANT_ENUM_PARAMS should cover you. Eric