boost.multiindex and addres of value as key

Question

I have a struct:

struct user_context {
   struct user_id;
   struct user_name;
   struct user_address;

   boost::int64_t user_id() const;
   const std::string& user_name() const;
};

I want to use boost.multiindex with three indexes: 1)user_id, 2)user_name, 3)address of the user_context object

I don't know, how to write key specification for address of the object of user_context type.

typedef std::shared_ptr<user_context> user_context_ptr;

typedef boost::multi_index::multi_index_container<
   user_context_ptr
   ,boost::multi_index::indexed_by<
       boost::multi_index::hashed_unique<
           boost::multi_index::tag<user_context::user_id>
          ,boost::multi_index::const_mem_fun<
              user_context
             ,boost::int64_t
             ,&user_context::user_id
           >
       >,
       boost::multi_index::hashed_unique<
          boost::multi_index::tag<user_context::user_name>
             ,boost::multi_index::const_mem_fun<
                 user_context
                ,const std::string&
                ,&user_context::user_name
             >
        >,
        boost::multi_index::hashed_unique<
           boost::multi_index::tag<user_context::user_address>
              ,boost::multi_index:: ??? <                      // <<<
                  user_context
                 ,user_context* (???)                          // <<<
                 ,???                                          // <<<
              >
          >
     >
> users_container;

Thanks.

Answer 1

Use boost::multi_index::identity<user_context_ptr>: two shared pointers are equivalent if they point to the same object (as it happens with regular pointers.)