Re: [boost] Possible bug with mpl::joint_view working on two mpl::maps

From: Martin Apel (martin.apel_at_[hidden])
Date: 2007-08-14 10:10:46

Aleksey Gurtovoy wrote:
> Martin Apel wrote in message news:46C19A4F.9080505_at_simpack.de...
>   
>> Aleksey Gurtovoy wrote:
>>     
>>> All in all, to get the behavior you want with the current library you
>>> need to actually merge two maps into a third one.
>>>       
> [...]
>
>   
>> I'm not sure, if I understand this correctly. What is the recommended
>> way of merging two maps into a third one? Is it possible with the
>> current MPL implementation?
>>     
>
> Sure.
>
>   
>> I only found an map::insert metafunction
>> to insert a single element, but not a whole range of pairs.
>>     
>
> You can actually to do something along these lines (untested):
>
> typedef copy<
>       joint_view<Map1,Map2>
>     , inserter< map0<>, insert<_1,_2> >
>     >::type JointMap;
>
> --
> Aleksey Gurtovoy
> MetaCommunications Engineering
>   
I still had no luck getting this to work. It seems that the typedef for
the joint map is OK (I had to change the insert to use a third
parameter as follows:

typedef copy<
   joint_view<Map1,Map2>,
   inserter <map0<>, insert<_1, end<_1>::type, _2> >
>::type JointMap;

otherwise it wouldn't compile).
However as soon as I try to access the result using

   std::cout << at<JointMap, int_<2> >::type::value << "\n";

I got tons of compile errors, from at_impl.hpp like the following:
error: no type named `type' in `struct boost::mpl::advance<mpl_::void_,
mpl_::int_<2> >'
and
advance_forward.hpp:42: error: no type named `type' in `struct
boost::mpl::next<mpl_::void_>'

It seems that at still is not happy with the type it is given.

Regards,

Martin

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