As Joaquín helped me out, I'm currently using his solution to test multi index containers. Playing with that, I'm now moving to hashed indices and 128 bits integers, just for fun. So now, in my class Data, I have a 128bit integer, indexed by most/half/least significant bits, with access functions. It works nicely. I added a fourth index, a hashed one, hashed by the MSB, and now I'd like to access all items that have MSB equal to 3, for instance. You will find my badly-written code below. Following the example [1], I proceeded in defining the index type, but here my compiler throws me two errors: error: missing 'typename' prior to dependent type name 'DataWithIndices::nth_index' ^ and error: expected unqualified-id typedef DataWithIndices::nth_index<3>::type byHashedIndex; ^ So I followed the suggestion and used typename, but an error is there: error: use 'template' keyword to treat 'nth_index' as a dependent template name typedef typename DataWithIndices::nth_index<3>::type byHashedIndex; ^ Again, I follow the suggestion, use template and it works. Adding the following line from the example gives me an error: error: expected expression byHashedIndex &p = multiIndex_.get<3>(); ^ error: declaration of reference variable 'p' requires an initializer byHashedIndex &p = multiIndex_.get<3>(); ^ Sincerely, I think I'm translating the example in a right manner, but obviously I am not. Can you help me? I am learning still, so please excuse me if this is trivial! Thanks & Cheers! === CODE === typedef boost::multi_index::multi_index_container< __uint128_t, boost::multi_index::indexed_by< boost::multi_index::ordered_non_unique<boost::multi_index::global_fun<__uint128_t, uint64, &Data::msb>>, boost::multi_index::ordered_non_unique<boost::multi_index::global_fun<__uint128_t, uint64, &Data::hsb>>, boost::multi_index::ordered_non_unique<boost::multi_index::global_fun<__uint128_t, uint64, &Data::lsb>>, boost::multi_index::hashed_non_unique<boost::multi_index::global_fun<__uint128_t, uint64, &Data::msb>> > > DataWithIndices; DataWithIndices multiIndex_; void objs() { typedef typename DataWithIndices::template nth_index<3>::type byHashedIndex; byHashedIndex &p = multiIndex_.get<3>(); } [1] http://www.boost.org/doc/libs/1_55_0/libs/multi_index/doc/tutorial/indices.h...