test_covariant.cpp

class IVec3 {
public:
    virtual ~IVec3() = default;
    virtual float x() const = 0;
    virtual float y() const = 0;
    virtual float z() const = 0;
    virtual IVec3* add(const IVec3& rhs) const = 0;
    virtual IVec3* clone() const = 0;
};

class Vec3 final : public IVec3 {
    float m_x, m_y, m_z;
public:
    Vec3() : m_x(0), m_y(0), m_z(0) {}
    Vec3(float x, float y, float z) : m_x(x), m_y(y), m_z(z) {}
    float x() const override { return m_x; }
    float y() const override { return m_y; }
    float z() const override { return m_z; }
    Vec3* add(const IVec3& rhs) const override {
        return new Vec3(m_x + rhs.x(), m_y + rhs.y(), m_z + rhs.z());
    }
    Vec3* clone() const override {
        return new Vec3(m_x, m_y, m_z);
    }
};

int main() {
    Vec3 a(1,2,3), b(4,5,6);
    IVec3* result = a.add(b);
    delete result;
    return 0;
}