[Boost-users] result_of protocol

Hello, I get the following msvc2008 error: error C2825: 'Holder': must be a class or namespace when followed by '::' in the following code ---------------------------------------------------------------------------------- struct extract_rule { template <typename Sig> struct result; template <typename Holder> struct result< extract_rule(const Holder) > { typedef const typename Holder::type& type; }; template <typename Holder> typename result< extract_rule(const Holder) >::type operator()( const Holder& h ) const { return h.rule; } }; ---------------------------------------------------------------------------------- 1> with 1> [ 1> Sig=extract_rule (const onevariantrule ) 1> ] The template onevariantrule<> is defined _before_ extract_rule. ------------------------------------------------------------------------------------------- template struct onevariantrule { typedef .... type; }; ------------------------------------------------------------------------------------------- Holder matches onevariantrule. That template instantiation is indeed a class. It has the inner field called "type". Any ideas would be appreciated,