class chess_board
{
public:
    chess_board(const std::pair<int, int>& white, const std::pair<int, int>& black)
        : white_{white},
        black_{black}
    {
        if (white == black) {
            throw std::domain_error("Both queens cannot occupy the same position.");
        }
    }

    chess_board()
    {}

    std::pair<int, int> white() const
    {
        return white_;
    }
    std::pair<int, int> black() const
    {
        return black_;
    }

private:
    const std::pair<int, int> white_ = std::make_pair(0, 3);
    const std::pair<int, int> black_ = std::make_pair(7, 3);
};