Hi Sebastian, Sebastian Redl escribió:
Hi,
I'm trying to implement property_tree in terms of multi_index, but have run into a problem.
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Now I want to use MultiIndex instead, so that I can have both the order of children preserved and offer O(log(N)) lookup of children. (The old code was O(N), but claimed to be O(log(N)).) But MultiIndex actually fails to instantiate with the incomplete type. More concretely, what fails to instantiate is the key retriever, a member<value_type, std::string, &value_type::first>. This is because the member access into the pair requires pair to be fully instantiated, and the instantiation fails as the ptree is incomplete.
Well, currently multi_index_containers are not guaranteed to be instantiable with incomplete types (analogously to stdlib containers: the std explicitly bans this possibility), so the following is basically undocumented behavior: try using a custom key extractor, just like shown in the following example: struct value_type; struct key_extractor; using namespace boost::multi_index; typedef multi_index_container< value_type, indexed_by< ordered_unique<key_extractor>
container;
struct value_type { value_type(int x):x(x){} int x; }; struct key_extractor:member<value_type,int,&value_type::x>{}; Hope this helps. Thanks for using Boost.MultiIndex. Joaquín M López Muñoz Telefónica, Investigación y Desarrollo