Re: [boost] [functional] Generic Selector for STL Pair's and Boost.Tuple's

From: Joel de Guzman (joel_at_[hidden])
Date: 2007-11-21 17:20:22

Dean Michael Berris wrote:

> So the idea is to use fusion::at_c<>() which I've been trying to avoid
> precisely because this static assert will fail:
> 
> BOOST_STATIC_ASSERT((
>   boost::is_same<
>     boost::result_of<select<0>(std::pair<int, int>)>::type,
>     int
>   >::value
> ));
> 
> This I think is because Fusion's at_c<>::type will return 'int const
> &' which is correct behavior as far as fusion goes, but not what I
> intend with the current implementation of select<> which is to return
> copies and not references. Perhaps it's going to be good to rethink
> this decision, and come up with select<> and select_copy<>.
> 

That's not a const-correctness problem. Fusion /at/ will return
int& which is the correct exact type that the at(s) function
returns.

See my other post. Use /value_at/ if you want the actual value! :-)

HTH,
-- 
Joel de Guzman
http://www.boost-consulting.com
http://spirit.sf.net