By "typelist", do you mean the template parameters (e.g. class T0, class T1, etc., in your code below)? If so, the following implements the member function: #include <boost/preprocessor/iteration/local.hpp> #include <boost/preprocessor/repetition/enum_params.hpp> #ifndef TYPELIST_MAX_SIZE #define TYPELIST_MAX_SIZE 7 #endif template <BOOST_PP_ENUM_PARAMS(TYPELIST_MAX_SIZE, class T)> IObject const * ObjectImpl::getInterface(InterfaceID const & iid) { IObject const * obj = 0; switch (iid) { case IObject::IID : { this->acquire(); obj = static_cast<IObject const *>(this); break; } #define BOOST_PP_LOCAL_LIMITS (0, TYPELIST_MAX_SIZE - 1) #define BOOST_PP_LOCAL_MACRO(n) \ case T ## n::IID: \ { \ this->acquire(); \ obj = static_cast<T const *>(this); \ break; \ } \ /**/ #include BOOST_PP_LOCAL_ITERATE() default : { throw InterfaceUnsupportedException(iid) break } } return obj; } Regards, Paul Mensonides _____ From: boost-users-bounces@lists.boost.org [mailto:boost-users-bounces@lists.boost.org] On Behalf Of Allen Gooch Sent: Wednesday, September 01, 2004 11:33 AM To: boost-users@lists.boost.org Subject: [Boost-users] Preprocessor lib question wrt to vertical repetition Given the following #include <boost/preprocessor/repetition/enum_params.hpp> #ifndef TYPELIST_MAX_SIZE # define TYPELIST_MAX_SIZE 7 #endif template <BOOST_PP_ENUM_PARAMS(TYPELIST_MAX_SIZE, class T)> class ObjectImpl : BOOST_PP_ENUM_PARAMS(TYPELIST_MAX_SIZE, public T), public ObjectBase<REFCNTR> { public: virtual Refcount acquire() const { return Base::acquire(); } virtual Refcount release() const { return Base::release(); } virtual Refcount getRefcount() const { return Base::getRefcount(); } virtual bool hasInterface(InterfaceID const & iid) const { return Base::hasInterface(iid); } virtual IObject * getInterface(InterfaceID const & iid) { IObject const * const_this = (IObject const *) this; return (IObject *) const_this->getInterface(iid); } virtual IObject const * getInterface(InterfaceID const & iid) { IObject const * obj = 0; switch (iid) { case IObject::IID : { this->acquire(); obj = static_cast<IObject const *>(this); break; } // Desired: for each type T in typelist generate the following case block // case T::IID : // { // this->acquire(); // obj = static_cast<T const *>(this); // break; // } default : { throw InterfaceUnsupportedException(iid) break } } return obj; } protected: ObjectImpl() { } virtual ~ObjectImpl() { } typedef ObjectBase<REFCNTR> Base; }; What is the best way to generate a case block for each type in the typelist? I've been looking at the Preprocessor appendix from the "C++ Template Metaprogramming" book (can't wait!) and see three different approaches to vertical repetition: local, file and self; however, I'm not clean on how to express what I want using these approaches. Can someone shed some light, or point me to an example in the Boost PP docs which solves a similar problem? Many thanks in advance. -allen