class SmartBuffer {
    size_t m_size;
    int* m_data;
public:
    friend void swap(SmartBuffer& first, SmartBuffer& second) noexcept {
        std::swap(first.m_size, second.m_size);
        std::swap(first.m_data, second.m_data);
    }
    SmartBuffer& operator=(SmartBuffer other) noexcept { // Pass by value (creates copy)
        swap(*this, other); // Swap with temporary copy
        return *this;
    } // Old data is safely destroyed when temporary 'other' leaves scope!
};