Re: [Boost-users] multi_index, best way to do insert_or_replace

bert hubert ha escrito:

Hi,

I misread (or didn't read) the boost::multi_index_container documentation and assumed 'insert' on a unique index would do 'replace', but of course it doesn't and shouldn't.

So, I've made this change:

- s_negcache.insert(ne); + + pair res=s_negcache.insert(ne); + if(!res.second) { + s_negcache.erase(res.first); + s_negcache.insert(ne); + }

But I can't help feeling there is probably a better and prettier way. Do people have any suggestions?

Hello Bert, You can do it more efficiently by using replace() instead of deleting and reinserting on collision. The following packages the entire procedure template<typename Index> std::pair replacing_insert(Index& i,const typename Index::value_type& x) { std::pair res=i.insert(x); if(!res.second)res.second=i.replace(res.first,x); return res; } So that you can say pair res=replacing_insert(s_negcache,ne); Note that replacing_insert() still cannot guarantee in the general case that insertion will always be succesful (hence its returning a pair): failure happens if two or more distinct elements are colliding with the value to be inserted. Check the attached code for an example of a failing call to replacing_insert(). HTH, Joaquín M López Muñoz Telefónica, Investigación y Desarrollo