From: Martin Apel (martin.apel_at_[hidden])
Date: 2007-08-14 02:38:03
Steven Watanabe wrote:
> Martin Apel <martin.apel <at> simpack.de> writes:
>> Hi all,
>> I have two mpl maps like this:
>> map<pair<int_<1>, int_<42> >,
>> pair<int_<2>, int_<43> >,
>> pair<int_<3>, int_<44> >
>> map<pair<int_<4>, int_<44> >,
>> pair<int_<5>, int_<45> >,
>> pair<int_<6>, int_<46> >
>> 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.
Thanks for the information, Steve. I didn't understand this from the
available docs. So is there another way of
joining two maps, so they create a single map, that can be used with
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