class foo {
 public:
	void reset() {
		a0.clear();
		a1.clear();
 	}
 private:
	std::set<int> a0, a1;
	std::set<int> b;
};


// |||||||||||||
// vvvvvvvvvvvvv
class reflefoo {
 public:
    void reset() {
		for (auto col : reflefoo::some_group_id)
        	col.reset();
    }
 private:
    some_group_id { std::set<int> s0, s1; }
    std::set<int> b;
};