From: Steven Watanabe (steven_at_[hidden])
Date: 2007-08-13 15:59:15
AMDG
Martin Apel <martin.apel <at> simpack.de> writes:
>
> Hi all,
>
> I have two mpl maps like this:
>
> typedef
> map<pair<int_<1>, int_<42> >,
> pair<int_<2>, int_<43> >,
> pair<int_<3>, int_<44> >
> > Map1;
>
> typedef
> map<pair<int_<4>, int_<44> >,
> pair<int_<5>, int_<45> >,
> pair<int_<6>, int_<46> >
> > Map2;
>
> I try to join them using "joint_view" as follows:
>
> typedef joint_view<Map1, Map2>::type JointMap;
>
> which works fine. Then I do
>
> std::cout << at<JointMap, int_<2> >::type::value << "\n";
>
> which gives the following compiler error:
>
> error: 'value' is not a member of 'boost::mpl::pair<mpl_::int_<3>,
> mpl_::int_<44> >'
>
> I tried this with gcc 3.4.6 and 4.2 under Linux, Boost version is 1.34.0.
> It seems "at" returns the entry after the searched entry, and not only
> the right half, but the complete pair.
>
> Has anybody got any hints on this? To me it looks like a bug in MPL, but
> I might be wrong.
>
joint_veiw is not intended to work that way for
maps. It just takes the two sequences and sticks
them together. The default implementation of at
which is used for joint_view returns the Nth element
of the sequence. Since you had the keys in order
starting at 1 it appeared that it was adding one.
The value of the key is irrelevant in determining
the result.
In Christ,
Steven Watanabe