[Boost-users] Re: multi_index and VC70 problem

From: Martin (adrianm_at_[hidden])
Date: 2005-04-05 10:11:34

> Hi Martin,
> 
> I haven't compiled your code, but I'm pretty confident
> the problem lies in the following: instead of
> 
>        composite_key<
>          BOOST_MULTI_INDEX_MEMBER(tTest, int, x)
>         ,BOOST_MULTI_INDEX_MEMBER(tTest, int, y)
>        )
> 
> you should write
> 
>        composite_key<
>         tTest
>         ,BOOST_MULTI_INDEX_MEMBER(tTest, int, x)
>         ,BOOST_MULTI_INDEX_MEMBER(tTest, int, y)
>        )
> 
> i.e. the first parameter of composite_key is the value
> to which the extractors are applied. Please let me know
> if that solves the issue.

That was a quick reply and you are correct. It is the first time I use 
composite keys and I followed the examples. My error was that I thought the 
first class argument in the examples meant the identity comparison. Looking at 
it now I understand how stupid that was.

> Other than that, I'm always eager to get feedback
> from users of the lib, so if you have additional comments
> or suggestions please let me know.

I work a lot with databases and I often have the need to store table like 
information in RAM. I often have a structure like

struct table_t {
  string key;
  std::vector<subtable_t> subtable;

};

The multi_index works perfectly for this.

The only thing I am missing is a way to update the non-key elements in-place.
Often my structures include subtables which means the copy can be expensive 
and I don't want to add member functions to update each member.

Currently I do

const_cast<std::vector<subtable>&>(itr->subtable).push_back(xxx);

It would be nice if there was a macro or template that could do it in a safe 
way, i.e. ensure index isn't changed.

nonkey(itr->subtable).push_back(xxx);