[Boost-users] Subject : [Multi-index] -- using a hashed unique index that is not part of the hashed value

Hello, what I basically want to do is using multi-index like a hashmap. I want to use vector<long> as key. However, all the examples I found are using member-fields of the values or the values themselves as key. Is it not possible to use multi-index like a hash_map<value,key> where the key is independent of the value type ? If yes, could someone please provide an example ? regards, Oliver