[Boost-users] boost::fusion zip_iterator and generic make_tuple call

Subject: [Boost-users] boost::fusion zip_iterator and generic make_tuple call
From: David Genest (david.genest_at_[hidden])
Date: 2009-03-13 10:20:48

Hi, 

I'm cross-posting here after a kind invitation from Joel.

I hope I can tap into your expert wisom! :-)

I have a fusion sequence of std::vectors which can be specified variably
by users: 

typedef boost::fusion::vector<std::vector, std::vector, ...> Inputs;

Using boost::zip_iterator, I would like to parallel iterate each
std::vector of the sequence and call a user function, but I am not sure
how to proceed. Of course I would like to do this in a generic manner so
that the user can change the number of inputs (std::vectors) at will.

My first non generic shot looks like this:

typedef boost::fusion::vector<std::vector<int>, std::vector<int> >
Inputs;
Inputs my_input;

struct UserFunction
{
    static void apply(int i, int j) { }
}

template<class F>
struct zip_func
{
    void operator() (const boost::tuple<int, int>& t) const
    {
        F::apply(t.get<0>(), t.get<1>());
    }
};

int main (int argc, char* argv[])
{
    using namespace boost::fusion;
    std::foreach(
              boost::make_zip_iterator(
                boost::make_tuple(
                    at_c<0>(my_input).begin(), 
                    at_c<1>(my_input).begin()),
              boost::make_zip_iterator(
                boost::make_tuple(
                    at_c<0>(my_input).end(), 
                    at_c<1>(my_input).end()),
              zip_func<UserFunction>())
    );
}

To the experts on the list:
I don't see how to generalize the zip_func operator() and make_tuple
call based on the fusion::vector signature. Is it even feasible, or is
my intuition leading me in a dead end? I saw that there is a
zip_iterator for fusion sequence in a svn branch
(http://svn.boost.org/svn/boost/branches/zip_iterator_fusion/), should I
go more in that direction? Any pointers would be appreciated.

Thank you for your time,

David.