Looking deeper into the iterator concept, one can see that it does not actually need to point to actual data; we could simply generate values on the fly. Here is a simple implementation of a forward iterator that generates integers on the fly. It only fulfills two iterator categories; forward_iterator and input_iterator:
class IntIterator {public: IntIterator(int v) : v_{v} {} auto operator==(const IntIterator& it)const{ return v_ == it.v_; } auto operator!=(const IntIterator& it)const{ return !(*this==it); } auto& operator*() const { return v_; } auto& operator++() { ++v_; return *this; }private: int v_{};};
The IntIterator can then be used to iterate an increasing range of integers just like if it was a container ...
