Re: [Boost-users] [multi_index].[composite_key] Index creation at run-time.

Prashant Thakre writes:

Hi, Guess, I should have given a code snippet :(

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But, how are you planning to actually implement this? Certainly you can't do the following: struct element { public: boost::tuple tp; // ... };

As per your first suggestion:

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1. If the maxium number of keys of the composite_key is bounded then you can use that maximum and later on, at run-time, take advantage of only the first N key slots. struct element { //Assumption: no more than 10 elements, a reasonable limit I guess. // boost::tuple tp; const std::string & tuple_element(const int ind) const { return tp.get<ind>; } //... };

Well, this can't work as is, cause tp.get<ind> requires that ind be a compile-time constant, which is not (it is an argument to tuple_element). Actually, I think it would be hard (though not impossible) to treat tuples, whose dimension is compile-time, as run-time sized objects. Let's turn to the second approach:

As per this suggestion:

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2. You can have std::vector<> as the key, the comparison semantics of this container in some ways resembles that of an infinite-length composite key. struct element { std::vector<const std::string > tp; const std::string & tuple_element(const int ind) const { return tp[ind]; } //... };

OK, here, instead of a composite_key instantiation, you can take advantage directly of std::vector comparison semantics (you don't really need tuple_element): typedef multi_index_container< element, indexed_by< hashed_unique< member > // other indices, maybe

element_collection;

Now, you can use n-sized vectors everywhere, where n is determined at run-time. Does this suit your needs? Joaquín M López Muñoz Telefónica, Investigación y Desarrollo