Null Iterator Adaptor

For pointers there is a nullptr definition. If we treat pointers analogous to geometric vectors, iterators may be treated as tensors. So, why don't we have a higher level nulliter ? This is the main idea behind this work.

null_iterator_adaptor is an iterator adaptor as its name declares. It converts any STL compatible iterator or simply pointer to a null pseudo iterator. So, what a null iterator does? Nothing. Or anything. It doesn't need a list to be used. It only uses type information of the underlying iterator. It has nothing to do with real data. It can be used to fool STL algorithms. It can be used as a null return value or a comparison to null constant for sequence traversing algorithms.

When it is used with STL algorithms as an output iterator it works as a null device. When used as an input iterator, it only gives out a default constructed value_type object. This behaviour is a bit like a zero device. It can be used as a random access iterator, it will access to infinity and beyond.

When a null iterator is assigned to a normal iterator, the assignment make the normal iterator default constructed. When null iterator is compared with a normal iterator, the comparison will be the comparison of the normal iterator with its default constructed state.

nulliter.hpp includes the null_iterator_adapter code. main.cpp includes some sample usage.

Tested with MinGW GCC 5.1 (TDM-GCC Distribution)

Some Examples

Sending data to nowhere

std::vector<int> dizi { 0, 1, 2, 3, 4, 5, 6, 7, 8, 9 };
std::copy(dizi.begin(), dizi.end(), make_null_iterator(dizi.begin()));

Using as a null return value

template<typename InputIt, typename T>
InputIt my_find( InputIt first, InputIt last, const T& value ) {
	using namespace nltr;
	InputIt result = std::find(first, last, value);
//	return (result != last) ? result : make_null_iterator((nullptr_t*)nullptr);
	return (result != last) ? result : nulliter;
}

int main() {

	using namespace nltr;

	std::vector<int> dizi { 0, 1, 2, 3, 4, 5, 6, 7, 8, 9 };

	for (int inx = 7; inx < 30; inx += 7) {
		std::cout << (inx % 15) << " is";
//		if (my_find(dizi.begin(), dizi.end(), (inx % 15)) == make_null_iterator((nullptr_t*)nullptr))
		if (my_find(dizi.begin(), dizi.end(), (inx % 15)) == nulliter)
			std::cout << " not";
		std::cout << " found in dizi" << std::endl;
	}
}

Please see main.cpp and nulliter.hpp for details. Compilation log (build.log) and output log (stdout.log) are also added.