Entry Generator

Prototype.cpp

#include <boost/iterator/iterator_facade.hpp>
#include <eigen3/Eigen/Core>
#include <iostream>
#include <tuple>
#include <vector>

using Entry = std::pair<Eigen::VectorXd, Eigen::VectorXi>;

class EntryIterator;

class EntryGenerator
{
public:
    virtual EntryIterator begin() = 0;
    virtual EntryIterator end() = 0;
    virtual bool valid() = 0;
    virtual void next() = 0;
    virtual Entry& get() = 0;
};

class EntryIterator : public boost::iterator_facade<EntryIterator, Entry, boost::single_pass_traversal_tag>
{
public:
    EntryIterator()
        : g()
    {
    }
    EntryIterator(EntryGenerator* g)
        : g(g)
    {
    }

private:
    friend class boost::iterator_core_access;
    Entry& dereference() const
    {
        if (!g || !g->valid())
            throw std::runtime_error("...");
        return g->get();
    }
    bool equal(EntryIterator const& l) const
    {
        return g == l.g || ((!g || !g->valid()) && (!l.g || !l.g->valid()));
    }
    void increment()
    {
        if (g)
            g->next();
    }

    EntryGenerator* g;
};

class CellEntryGenerator : public EntryGenerator
{
public:
    CellEntryGenerator()
    {
        Eigen::Vector3d values;
        values << 4.0, 2.7, 4.2;
        Eigen::Vector3i numbers;
        numbers << 1, 2, 3;
        entries.push_back(std::make_pair(values, numbers));
        entries.push_back(std::make_pair(values, numbers));
        entries.push_back(std::make_pair(values, numbers));
        entries.push_back(std::make_pair(values, numbers));
    }

    bool valid() override
    {
        return current_entry < entries.size();
    }
    void next() override
    {
        current_entry++;
    }
    Entry& get() override
    {
        return entries[current_entry];
    }

    EntryIterator begin() override
    {
        return EntryIterator(this);
    }
    EntryIterator end() override
    {
        return EntryIterator();
    }

private:
    std::vector<Entry> entries;
    int current_entry = 0;
};

int main()
{
    CellEntryGenerator generator;
    for (Entry& vecPlusNumbering : generator)
    {
        std::cout << "Values of this cell:\n" << vecPlusNumbering.first << std::endl;
        std::cout << "Numbering of these values:\n" << vecPlusNumbering.second << std::endl;
    }

    return 0;
}