イテレーションしつつインデックスるも取るコード

withIndex.cpp

#include <iostream>
#include <vector>

/* -- ここから -- */
template<typename T, typename C = int>
class Element
{
    template<typename S>
    friend class Iterator;

private:
    inline void set(const C i, T &v)
    {
        index = i;
        value = v;
    }

public:
    C index;
    T &value;

    inline Element(const C idx, T &val) : index(idx), value(val) { }
};

template<typename T>
class Iterator
{
    typedef typename T::iterator iter_type;
    typedef Element<typename T::value_type> elem_type;

private:
    int index;
    iter_type iterator;
    elem_type elem;

public:
    inline Iterator(iter_type it) : index(0), iterator(it), elem(0, *it) { }

    inline bool operator!=(const Iterator<T> &it) const { return iterator != it.iterator; }

    inline elem_type &operator*() { return elem; }
    inline elem_type *operator->() { return &(operator*());}

    inline const Iterator &operator++()
    {
        elem.set(++index, *(++iterator));
        return *this;
    }
};

template<typename T>
class WithIndex
{
public:
    typedef Iterator<T> iterator;
private:
    T &iterable;

public:
    inline WithIndex(T &iterable) : iterable(iterable) { }
    inline Iterator<T> begin() const { return Iterator<T>(iterable.begin()); }
    inline Iterator<T> end() const { return Iterator<T>(iterable.end()); }
};

template<typename T>
inline WithIndex<T> withIndex(T &iterable) { return WithIndex<T>(iterable); }

/* -- ここまで -- */

int main(int argc, const char * argv[])
{
    std::vector<int> iv = { 2, 4, 6, 8, 10 };

    for(auto &e : withIndex(iv)) // インデックスも取る!
    {
        std::cout << e.index << ": " << e.value << std::endl;
    }
    return 0;
}