Defines a lazy/delayed dataset store.

namespace boost {
  namespace unit_test {
    namespace data {

      // Delayed dataset instanciation. 
      template<typename dataset_t, class ... Args> 
        std::enable_if< monomorphic::is_dataset< dataset_t >::value, monomorphic::delayed_dataset< dataset_t, Args... > >::type 
        make_delayed(Args... args);
      namespace monomorphic {
        template<typename dataset_t, class ... Args> class delayed_dataset;

        template<typename dataset_t, class ... Args> 
          struct is_dataset<delayed_dataset< dataset_t, Args... >>;
      }
    }
  }
}