#include <string>

class dummy {
public:
    explicit dummy(int const& i)
        : s_ { "Hello world" }
        , val_ { i }
    {
    }
    explicit dummy()
        : dummy(5)
    {
    }
    std::string const& get_s()
    {
        return s_;
    }
    int get_val()
    {
        return val_;
    }

private:
    std::string s_;
    const int val_;
};

auto main() -> int
{
    dummy d1(5);
    dummy d2 {};
}