flat_expression_templates.cpp

template <class F, class... Ts>
struct O_Om
{
	std::tuple<Ts...> nodes;

	gut::member_result_t<F, decltype(std::get<1>(nodes).clone()),
	                     decltype(std::get<0>(nodes).clone())> state;
	template <class A, class... Us>
	constexpr O_Om(A&& state, Us&&... args)
		: nodes{fw(args)...}, state{fw(state)}
	{
	}

  	/* nested iterator type here */
  
	iterator begin() { return iterator(state, 0, nodes); }
	iterator end() { return iterator(state, sizeof...(Ts), nodes); }

	constexpr decltype(auto) yield()
	{
		for (std::size_t i(1); i < sizeof...(Ts); ++i)
		{
			state = vtu::call_with_tuple_element_first(
				F{}, nodes, i, state);
		}

		return state;
	}
};