[Boost-users] [multi_index] using boost::tuple and hash_unique

From: Ovanes Markarian (om_boost_at_[hidden])
Date: 2007-04-23 12:11:05

Hello,

unfortunately I can't figure out how to specify member access for a hash function to a hash
indexed mult-index container containing boost::tuple. I would like to hash by the first tuple
member only. Can someone help?

Here is an example:

typedef boost::tuples::tuple<std::string, int, some_other_type>    my_tuple;

struct hash {};

multi_index_container<
   my_tuple
   , indexed_by<
       hashed_unique<tag<hash>, ????
       , other_index_type...
     >
   >                                      hashed_container;

I would like this tuple to be hashed by the first member. boost::tuple has no access member
function to the first member. The only way to access it is:

my_tuple t("aaa", 10, xyz);

std::string s(get<0>(t));

but as I can see the doc for multi_index it supports only access through a member function or by
using the hash function which is applied to the whole object. The second scenario does not suit
well, since I must pass an object instance to the hasher, where I would like to pass a name only.
Should I write my own key_extractor class? Any help is appreciated.

With Kind Regards,

Ovanes