Idiom：Copy-and-swap

简单的实现：

class Myclass {
public:
  Myclass(size_t size) : data_(size ? new(std::nothrow) int[size] : nullptr) , size_(!data_ ? 0 : size){}
  Myclass(const Myclass& other) {
    data_ = other.size_ ? new(std::nothrow) int[other.size_] : nullptr;
    size_ = !data_ ? 0 : other.size_;
  }
  Myclass& operator=(Myclass other) {
    Swap(other);
    return *this;
  }
  void Swap(Myclass& other) noexcept {
    std::swap(data_, other.data_);
    std::swap(size_, other.size_);
  }
private:
  int* data_;
  size_t size_;
};