[Boost-users] Pushing iterators to far?

10 Jan 2013

      Hi All,

I'm trying to do some slightly hooky stuff with the iterators library and
cannot get the following code to compile.

When the second last line of main is uncommented ("ZIter iter(b);"),
compilation fails.

The error mesages suggest this is a problem with determining the
appropriate traversal category of "ZIter".

Can anyone advise if this is problem with my code, a bug, am I asking too
much of the library, ...?

Cheers,
Simon Knapp.

compiler:
Visual Studio 2008 - version 9.0.30729.1 SP

//----------------------------------------------------------------------------------------------------------------------------
// begin iterator_tests.cpp
//----------------------------------------------------------------------------------------------------------------------------
#include <vector>

#include <boost/iterator/filter_iterator.hpp>
#include <boost/iterator/zip_iterator.hpp>
#include <boost/tuple/tuple.hpp>

typedef std::vector<long long> LLGrid;
typedef std::vector<float> FloatGrid;

typedef LLGrid::const_iterator LLGridIter;
typedef FloatGrid::const_iterator FloatGridIter;

typedef boost::tuples::tuple<LLGridIter, FloatGridIter> IDAndAreaTuple;
typedef boost::zip_iterator<IDAndAreaTuple> IDAndAreaIterator;
typedef std::iterator_traits<IDAndAreaIterator>::reference IDAndAreaRef;

struct Fnctr {
    bool operator()(const IDAndAreaRef ref) const {
        return true;
    }
};

typedef boost::filter_iterator<Fnctr, IDAndAreaIterator> FIter;
typedef boost::tuples::tuple<FloatGridIter, FIter> ZIterTuple;
typedef boost::zip_iterator<ZIterTuple> ZIter;

static ZIterTuple makeZIterTuple(
    Fnctr const& fnctr,
    LLGridIter const& beginIdGrid,
    LLGridIter const& endIdGrid,
    FloatGridIter const& beginAreaGrid,
    FloatGridIter const& endAreaGrid,
    FloatGridIter const& gtgdIter
    ) {
    return
        boost::make_tuple(
            gtgdIter,
            boost::make_filter_iterator(
                fnctr,
                boost::make_zip_iterator(boost::make_tuple(beginIdGrid,
beginAreaGrid)),
                boost::make_zip_iterator(boost::make_tuple(endIdGrid,
endAreaGrid))
            )
        );
}

int main(int argc, char* argv[]) {
    FloatGrid areaMask, regionStat;
    LLGrid regionMask;
    ZIterTuple b(makeZIterTuple(Fnctr(), regionMask.begin(),
regionMask.end(), areaMask.begin(), areaMask.end(), regionStat.begin()));
    //ZIter iter(b);
    return 0;
}
//----------------------------------------------------------------------------------------------------------------------------
// end iterator_tests.cpp
//----------------------------------------------------------------------------------------------------------------------------