From 39318cf12bde973d0880b02ada5dfed06320b77e Mon Sep 17 00:00:00 2001
From: "Joshua Moerman (@Kassalade)" <lakseru@gmail.com>
Date: Sun, 22 May 2011 17:13:03 +0200
Subject: [PATCH] first draft of counting range-based-for-loops

---
 iterators/counting_iterator.hpp | 97 +++++++++++++++++++++++++++++++++
 iterators/main.cpp              | 21 +++++++
 2 files changed, 118 insertions(+)
 create mode 100644 iterators/counting_iterator.hpp
 create mode 100644 iterators/main.cpp

diff --git a/iterators/counting_iterator.hpp b/iterators/counting_iterator.hpp
new file mode 100644
index 0000000..462ab86
--- /dev/null
+++ b/iterators/counting_iterator.hpp
@@ -0,0 +1,97 @@
+/*
+
+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);
+}
+
diff --git a/iterators/main.cpp b/iterators/main.cpp
new file mode 100644
index 0000000..7b9f8d0
--- /dev/null
+++ b/iterators/main.cpp
@@ -0,0 +1,21 @@
+#include "counting_iterator.hpp"
+#include <vector>
+#include <iostream>
+
+int main(){
+	std::vector<int> v{1,3,37,1337,7};
+
+	for(auto x : counted(v)){
+		std::cout << "v[" << x.index << "] = " << x.value << std::endl;
+	}
+
+	for(auto x : counted(v)){
+		x.value *= x.index;
+	}
+
+	for(auto x : counted(v)){
+		std::cout << "v[" << x.index << "] = " << x.value << std::endl;
+	}
+
+	return 0;
+}