Hello, I have the MPL book and I've used some metaprogramming before but I'm always at the edge of my understanding of the language when I do it. I have a problem right now which I suspect is trivial but I can't for the life of me figure out how to do it. I have a list of 25 resource types (class Sound, class Script, etc.) and since they are not mutable I want to share them so I have a resource cache template that looks something like: template< typename Resource > class Cache { public: typedef typename Tag<Resource>::type resource_tag; /// Retrieve a resource by id /// Throws cache_error if the resource couldn't be found in the Repository Resource& Retrieve( ResourceId id ) { // is the resource in the cache? typename ResourceMap::iterator it = m_resources.find( id ); if( it != m_resources.end() ) { return it->second; } else { return LoadResource( id ); } } /// Clears the cache and destructs all cached resources. void Clear() { m_resources.clear(); } private: Resource& LoadResource( ResourceId id ) { Stream stream( Repository::Instance().Retrieve( id, resource_tag::type::value ) ); if( !stream.fail() ) { Resource* res = new Resource(stream); m_resources.insert( id, res ); return *res; } else { throw cache_error( id, resource_tag::type::value ); } } typedef boost::ptr_map< ResourceId, Resource > ResourceMap; ResourceMap m_resources; }; I have a class which must contain a Cache for each of the 25 resource types and support calls to get a resource of a particular type given an id and be able to call Clear on all 25 caches. Something like class Manager { public: /// Returns Cache<Resource>::Retrieve( id ) template< typename Resource > const Resource& Get( ResourceId id ); /// Calls Cache::Clear for all resource types void Clear(); }; It would be pretty easy to just copy and paste it out 25 times but I would like to reduce code duplication and simplify maintenance through metaprogramming. I have a private boost::mpl::list25 named resource_list containing all the resource types. I think I need to transform that in to a boost::fusion::map of 25 Resource to Cache<Resource> pairs but I'm not sure that is what I really need to do or how to go about doing that. Thanks, Michael Marcin