#include <iostream>
#include <memory>
#include <string>
#include <vector>
using namespace std;
 
class Test {
private:
    string _name;
    vector<unique_ptr<Test>> _list;
public:
    explicit Test(const string& S) : _name(S) { }
 
    string to_string() const {
        string s("[");
        s += _name;
 
        for (auto const& p : _list) {
            s += ",";
            s += p->to_string();
        }
 
        s += "]";
        return s;
    }
 
    Test& add(const string& S) {
        _list.push_back(make_unique<Test>(S));
        return *(_list.back());
    }
};
 
int main() {
    Test x("one");
    x.add("two");
    Test& y = x.add("three");
    y.add("four");
 
    cout << y.to_string() << '\n';
    cout << x.to_string() << '\n';
}
 

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