----- Mensaje original ----- De: Rob Stewart <stewart@sig.com> Fecha: Lunes, Abril 26, 2004 10:16 pm Asunto: Re: [boost] [multi_index] composite keys: request for advice
From: Joaquin M Lopez Munoz <joaquin@tid.es>
Composite keys can be specified by a new construct called composite_key in the following manner:
struct record { int first; int second int third; };
multi_index_container< record, indexed_by< composite_key< record, //base value member<record,int,&record::first>, // first key
Would that you could make this work to avoid the duplication and chance for errors:
member< &record::first >
I know a function template can deduce the other types, but I can't think of how to make it work here.
I'd be the happiest man on the block if I could have that, but AFAIK it is not possible. The fact that member<> is here specified in the context of composite_key does not help, either. This has been previously brought into discussion several times. If you have a typeof() utility and don't object to some macro hackery, this is an approximation: template<typename Class,typename Member> Class base_from_ptr_to_member(Member Class::*); template<typename Class,typename Member> Member member_from_ptr_to_member(Member Class::*); #define BOOST_MULTI_INDEX_SMART_MEMBER(PtrToMember) \ member< \ typeof(base_from_ptr_to_member(PtrToMember)),\ typeof(member_from_ptr_to_member(PtrToMember)),\ PtrToMember\
... multi_index_container< record, indexed_by< ordered_unique< BOOST_MULTI_INDEX_SMART_MEMBER(&record::x) >
Joaquín M López Muñoz Telefónica, Investigación y Desarrollo