What if the composite key should be parameterized from a file? In the case of <raw> struct phonebook_entry{ std::string family_name; std::string given_name; std::string phone_number; phonebook_entry( std::string family_name, std::string given_name, std::string phone_number): family_name(family_name),given_name(given_name),phone_number(phone_number) {}}; // define a multi_index_container with a composite key on // (family_name,given_name)typedef multi_index_container< phonebook_entry, indexed_by< //non-unique as some subscribers might have more than one number ordered_non_unique< composite_key< phonebook_entry, member, member > >, ordered_unique< // unique as numbers belong to only one subscriber member >

...

phonebook;

</raw> the lines member, member should be auto-generated by reading a composite key from a file. 2014-02-04 Jason [via Boost] :

On 02/04/2014 03:36 PM, syvyi wrote:

...

Hello,

there's a structure struct person { std::string name; std::string surname; int birth_year; std::string craft; };

How to create such a multiindex container that dumping could performed using an index as name, surname and year triple alltogether? Sounds like you might be interested in MultiIndex's composite key feature:

http://www.boost.org/doc/libs/1_55_0/libs/multi_index/doc/tutorial/key_extra...

Jason _______________________________________________ Boost-users mailing list [hidden email] http://user/SendEmail.jtp?type=node&node=4658955&i=0 http://lists.boost.org/mailman/listinfo.cgi/boost-users

------------------------------ If you reply to this email, your message will be added to the discussion below:

http://boost.2283326.n4.nabble.com/Boost-MultiIndex-Using-several-keys-toget... To unsubscribe from Boost.MultiIndex. Using several keys together., click herehttp://boost.2283326.n4.nabble.com/template/NamlServlet.jtp?macro=unsubscribe_by_code&node=4658953&code=YWxleGFuZGVyLnN2a0BnbWFpbC5jb218NDY1ODk1M3wxMzU1MTY0OTM5 . NAMLhttp://boost.2283326.n4.nabble.com/template/NamlServlet.jtp?macro=macro_viewer&id=instant_html%21nabble%3Aemail.naml&base=nabble.naml.namespaces.BasicNamespace-nabble.view.web.template.NabbleNamespace-nabble.view.web.template.NodeNamespace&breadcrumbs=notify_subscribers%21nabble%3Aemail.naml-instant_emails%21nabble%3Aemail.naml-send_instant_email%21nabble%3Aemail.naml

-- View this message in context: http://boost.2283326.n4.nabble.com/Boost-MultiIndex-Using-several-keys-toget... Sent from the Boost - Users mailing list archive at Nabble.com.

syvyi writes:

What if the composite key should be parameterized from a file?

OK, this can be done, but you need to move some of the container definition components from compile time to run time. The following typedef std::function any_person_extractor; defines a polymorhpic key extractor on person: something that takes a person and return something (which we wrap in a boost::any object, since we won't know what this something is until run time.) Similarly, typedef std::function< bool(const boost::any&,const boost::any&)> any_compare; is a polymorphic wraper for compare objects taking boost::any's: each compare objects we feed into any_compare will have to know what's inside these boost::any's to do the proper comparison, which we can do with template<typename T> struct any_less { bool operator()(const boost::any& x,const boost::any& y)const { return boost::any_cast<T>(x) struct any_less<void> { bool operator()(const boost::any& x,const boost::any& y)const {return false;} }; Now, let's define the multi_index_container instantiation as: typedef multi_index_container< person, indexed_by< ordered_non_unique< composite_key< person, any_person_extractor, any_person_extractor, any_person_extractor, any_person_extractor >, composite_key_compare< any_compare, any_compare, any_compare, any_compare > >

person_container;

What we are doing here is reserve 4 slots (we can have more, of course) to fill at run time with specific key extractors (and their corresponding compare objects.) For instance, the following person_container c( boost::make_tuple( boost::make_tuple( boost::make_tuple( any_person_extractor(member()), any_person_extractor(member()), any_person_extractor( member()), void_person_extractor() ), boost::make_tuple( any_less<int>(), any_lessstd::string(), any_lessstd::string(), any_less<void>() ) ) )); instantiates a person_container with a composite key having three extractors on birth year, name and surname (a more elaborate example would fetch the info on which extractors toprovide from a configuration file or something); the remainng slot we fill with our dummy key extractor and compa object. Once instantiated, c can be used as a normal (compile-time defined) container. for instance, the following retrieves the persons born in 1959: std::pair p= c.equal_range(1959); If the first key extractor weren't compatible with the int we've provided, for instance if we'd passed a string, a boost:any exception would be thrown --that's the price we pay for having this run-time flexibility, lack of compile time type checkhing. And that's it. You can play with a full example at http://coliru.stacked-crooked.com/a/4fa76b314298516d Joaquín M López Muñoz Telefónica Digital