it-works/iterators/counting_iterator.hpp

/*

USAGE:
"for(auto x : counted(v)) { ... x.value ... x.index ... }"
x.value is a reference to the element in the container (so you can change it's value), x.index is what it is.
Container should havae forward iterators.

NOTE:
This headers is purely a handy tool for the "for(auto x : counter(v))"-syntax. Using it explicitly with iterators is not recommended!

NOTE:
There is no const version of it. Doing "for(const auto x : counted(v))" doesn't make it impossible to change x (so the element in the container can be modified).

*/
#include <iterator>

// A reference is a struct, yuk...
// Maybe a proxy is better
template <typename T, typename Integer>
struct counting_pair{
private:
	typedef counting_pair self;

public:
	T& value;
	Integer index;

	counting_pair(T& v, Integer i) : value(v), index(i) {}
	counting_pair(const self& copy) : value(copy.value), index(copy.index) {}
};

// It's only forward for the moment
template <typename Iterator, typename Integer>
struct counting_iterator : public std::iterator<std::forward_iterator_tag, counting_pair<typename std::iterator_traits<Iterator>::value_type, Integer>> {
private:
	typedef counting_iterator self;
	typedef counting_pair<typename std::iterator_traits<Iterator>::value_type, Integer> value_type;

	Iterator it;
	Integer count;

public:
	counting_iterator(Iterator it) : it(it), count(0) {}
	counting_iterator(const self& copy) : it(copy.it), count(copy.count) {}

	self& operator++(){
		++it;
		++count;
		return *this;
	}

	self operator++(int){
		self copy(*this);
		++*this;
		return copy;
	}

	bool operator==(const self& rhs){
		return it == rhs.it;
	}

	bool operator!=(const self& rhs){
		return it != rhs.it;
	}

	typename self::value_type operator*() {
		return counting_pair<typename std::iterator_traits<Iterator>::value_type, Integer>(*it, count);
	}
};

template <typename Container, typename Integer>
struct counting_container {
private:
	typedef counting_container self;
	typedef typename Container::iterator backing_iterator;
	Container* backing_container;

public:
	typedef counting_iterator<backing_iterator, Integer> iterator;

	counting_container(Container& v) : backing_container(std::addressof(v)) {}
	counting_container(const self& x) : backing_container(x.backing_container) {}

	iterator begin() {
		return iterator(backing_container->begin());
	}

	iterator end() {
		return iterator(backing_container->end());
	}
};

template <typename Integer = int, typename Container>
counting_container<Container, Integer> counted(Container& c){
	return counting_container<Container, Integer>(c);
}