public:

behavior_stack_mover(behavior_stack* st) : m_stack(st) { }

behavior_stack_mover& operator=(behavior_stack::element_type&& rval) {

m_stack->m_erased_elements.emplace_back(move(rval.first));

return *this;

}

behavior_stack_mover& operator*() { return *this; }

behavior_stack_mover& operator++() { return *this; }

behavior_stack_mover operator++(int) { return *this; }

private:

behavior_stack* m_stack;

if (expected_response.valid()) {

auto e = m_elements.rend();

auto i = find_if(m_elements.rbegin(), e, [=](element_type& val) {

return val.second == expected_response;

});

if (i != e) return i->first;

}

return none;

if (m_elements.empty()) { } // nothing to do

else if (!m_elements.back().second.valid()) erase_at(m_elements.end() - 1);

else rerase_if([](const element_type& e) {

return e.second.valid() == false;

});

if (m_elements.empty() == false) {

move(m_elements.begin(), m_elements.end(), move_iter(this));

m_elements.clear();

}