expr_iterator.cpp

class iterator
{ // Publicly define the standard typedefs
	reference _state;
	std::size_t _pos;
	std::tuple<Ts...>& _nodes;

public:
	iterator(reference state, std::size_t pos,
        	 std::tuple<Ts...>& nodes)
		: _state(state), _pos(pos), _nodes(nodes) 
	{}
	iterator(const iterator& other)
		: _state(other._state)
		, _pos(other._pos)
		, _nodes(other._nodes) 
	{}
	iterator& operator=(const iterator& other) {
		_state = other._state;
		_pos   = other._pos;
		_nodes = other._nodes;
		return *this;
	}
	bool operator==(const iterator& other) const { return _pos == other._pos; }
	bool operator<(const iterator& other) const { return _pos < other._pos; }
	iterator& operator++() {
		++_pos;
		_state = vtu::call_with_tuple_element_first(F{}, _nodes,
							    _pos, _state);
		return *this;
	}
	reference operator*() const { return _state; }
	pointer operator->() const { return &_state; }
};