#include <iostream>
#include <vector>
#include <memory>

template <class ApparentElemType> class readonly_vector_view_base;

template <class ApparentElemType>
class readonly_vector_view
{
  public:
    readonly_vector_view(const readonly_vector_view& other) : pimpl(other.pimpl) {}
    readonly_vector_view(std::shared_ptr<readonly_vector_view_base<ApparentElemType>> pimpl_) : pimpl(pimpl_) {}

    typedef typename readonly_vector_view_base<ApparentElemType>::iter iter_base;
    class iter
    {
      public:
        iter(std::unique_ptr<iter_base> it_) : it(it_->clone()) {}
        iter(const iter& other) : it(other.it->clone()) {}
        iter& operator=(iter& other) { it = other.it->clone(); return *this; }

        ApparentElemType operator*() const { return **it; }
        iter& operator++() { ++*it; return *this; }
        iter& operator--() { --*it; return *this; }
        iter operator++(int) { iter n(*this); ++*it; return n; }
        iter operator--(int) { iter n(*this); --*it; return n; }
        bool operator== (const iter& other) const { return *it == *other.it; }
        bool operator!= (const iter& other) const { return *it != *other.it; }
      private:
        std::unique_ptr<iter_base> it;
    };

    iter begin() { return iter(pimpl->begin()); }
    iter end() { return iter(pimpl->end()); }
  private:
    std::shared_ptr<readonly_vector_view_base<ApparentElemType>> pimpl;
};

template <class ApparentElemType>
struct readonly_vector_view_base
{
    struct iter
    {
        virtual std::unique_ptr<iter> clone() const = 0;

        virtual ApparentElemType operator*() const = 0;
        virtual iter& operator++() = 0;
        virtual iter& operator--() = 0;
        virtual bool operator== (const iter& other) const = 0;
        virtual bool operator!= (const iter& other) const = 0;
        virtual ~iter(){}
    };

    virtual std::unique_ptr<iter> begin() = 0;
    virtual std::unique_ptr<iter> end() = 0;

    virtual ~readonly_vector_view_base() {}
};

template <class ElemType, class ApparentElemType>
struct readonly_vector_view_impl : readonly_vector_view_base<ApparentElemType>
{
    typedef typename readonly_vector_view_base<ApparentElemType>::iter iter_base;

    readonly_vector_view_impl(std::shared_ptr<std::vector<ElemType>> vec_) : vec(vec_) {}

    struct iter : iter_base
    {
        std::unique_ptr<iter_base> clone() const { std::unique_ptr<iter_base> x(new iter(it)); return x; }

        iter(typename std::vector<ElemType>::iterator it_) : it(it_) {}

        ApparentElemType operator*() const { return *it; }
        iter& operator++() { ++it; return *this; }
        iter& operator--() { ++it; return *this; }

        bool operator== (const iter_base& other) const {
            const iter* real_other = dynamic_cast<const iter*>(&other);
            return (real_other && it == real_other->it);
        }
        bool operator!= (const iter_base& other) const { return ! (*this == other); }

        typename std::vector<ElemType>::iterator it;
    };

    std::unique_ptr<iter_base> begin() {
        iter* x (new iter(vec->begin()));
        std::unique_ptr<iter_base> y(x);
        return y;
    }
    std::unique_ptr<iter_base> end() {
        iter* x (new iter(vec->end()));;
        std::unique_ptr<iter_base> y(x);
        return y;
    }

    std::shared_ptr<std::vector<ElemType>> vec;
};


struct A
{
    A(int x_) : x(x_) {};

    readonly_vector_view<A*> test() { return test_A(); }
    virtual readonly_vector_view<A*> test_A() = 0;

    int x;
};

struct B : A
{
    B (int y_, int x_) : y(y_), A(x_) {}
    B() : A(0), bvec(std::make_shared<std::vector<B*>>())
    {
        bvec->push_back (new B(2,3));
        bvec->push_back (new B(4,5));
        bvec->push_back (new B(6,7));
    }
    std::shared_ptr<std::vector<B*>> bvec;

    readonly_vector_view<B*> test() { return test_B(); }

    virtual readonly_vector_view<A*> test_A() {
        return readonly_vector_view<A*>(std::make_shared<readonly_vector_view_impl<B*, A*>>(bvec));
    }
    virtual readonly_vector_view<B*> test_B() {
        return readonly_vector_view<B*>(std::make_shared<readonly_vector_view_impl<B*, B*>>(bvec));
    }

    int y;
};

int main ()
{
    B b;
    A& a (b);

    readonly_vector_view<A*>va = a.test();
    readonly_vector_view<B*>vb = b.test();

    for (readonly_vector_view<A*>::iter pa = va.begin(); pa != va.end(); ++pa)
    {
        std::cout << (*pa)->x << " ";
    }
    std::cout << std::endl;
    for (readonly_vector_view<B*>::iter pb = vb.begin(); pb != vb.end(); ++pb)
    {
        std::cout << (*pb)->x << ":" << (*pb)->y << " ";
    }
    std::cout << std::endl;
}