C++ Primer（第5版） 练习 16.29
练习 16.29 修改你的Blob类，用你自己的shared_ptr代替标准库中的版本。
环境：Linux Ubuntu（云服务器）
工具：vim
代码块
template <typename> class BlobPtr;
template <typename> class Blob;
template <typename T> bool operator==(const Blob<T>&, const Blob<T>&);template <typename T>class Blob {friend class BlobPtr<T>;friend bool operator==<T>(const Blob<T>&, const Blob<T>&);public:typedef T value_type;typedef typename std::vector<T>::size_type size_type;Blob();Blob(std::initializer_list<T> il);size_type size() const { return data->size(); }bool empty() const { return data->empty(); }void push_back(const T& t) { data->push_back(t); }void push_back(T&& t) { data->push_back(std::move(t)); }void pop_back();T& back();T& operator[](size_type i);private:SharedPtr<std::vector<T>> data;void check(size_type i, const std::string& msg) const;
};template <typename T> void Blob<T>::check(size_type i, const std::string& msg) const {if (i >= data->size()) {throw std::out_of_range(msg);}
}template <typename T> T& Blob<T>::back() {check(0, "back on empty Blob");return data->back();
}template <typename T> T& Blob<T>::operator[](size_type i) {check(i, "subscript out of range");return (*data)[i];
}template <typename T> void Blob<T>::pop_back() {check(0, "pop_back on empty Blob");data->pop_back();
}template <typename T> Blob<T>::Blob() : data(SharedPtr<std::vector<T>>(new std::vector<T>())) {}template <typename T> Blob<T>::Blob(std::initializer_list<T> il): data(SharedPtr<std::vector<T>>(new std::vector<T>(il))) {}template <typename T> class BlobPtr {public:BlobPtr() : curr(0) {}BlobPtr(Blob<T>& a, size_t sz = 0) : wptr(a.data), curr(sz) {}T& operator*() const {auto p = check(curr, "dereference past end");return (*p)[curr];}BlobPtr& operator++();BlobPtr& operator--();private:std::size_t curr;WeakPtr<std::vector<T>> wptr;SharedPtr<std::vector<T>> check(std::size_t, const std::string&) const;
};template <typename T> SharedPtr<std::vector<T>> BlobPtr<T>::check(std::size_t i, const std::string& msg) const {auto ret = wptr.lock();if (!ret) {throw std::runtime_error("unbound BlobPtr");}if (i >= ret->size()) {throw std::out_of_range(msg);}return ret;
}template <typename T> BlobPtr<T>& BlobPtr<T>::operator++() {check(curr, "increment past end of BlobPtr");++curr;return *this;
}template <typename T> BlobPtr<T>& BlobPtr<T>::operator--() {--curr;check(curr, "decrement past begin of BlobPtr");return *this;
}
