Hi : I'm just starting to use boost utility library and it seems very promising. I am trying to define a new multi_index type and gcc it's giving me error messages. First I properly added the includes for boost::multi_index : #include <boost/multi_index_container.hpp> #include <boost/multi_index/mem_fun.hpp> #include <boost/multi_index/hashed_index.hpp> then the includes for "Item" and "ObjectId" declarations: #include "Item.h" following that appears this: typedef multi_index_container< Item*, indexed_by< hashed_unique<mem_fun<Item, ObjectId, &Item::getId> > > > ItemsContainer; When I try to compile this code gcc reports the following errors: error: 'mem_fun' was not declared in this scope error: template argument 1 is invalid error: type/value mismatch at argument 3 in template parameter list for 'template<class Arg1, class Arg2, class Arg3, class Arg4> struct boost::multi_index::hashed_unique' error: expected a type, got '&emedia::lumiere::Item::getId' error: template argument 1 is invalid error: template argument 2 is invalid error: expected unqualified-id before '>' token It seems that I'm forgetting something. It's very strange because I all ready compilled this code in another project but I can't find any difference with this one. Any idea. Thanks in advance. René