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Copy pathBlob.h
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111 lines (94 loc) · 2.62 KB
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#ifndef BLOB_H_INCLUDED
#define BLOB_H_INCLUDED
template <typename T>
class Blob
{
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:
std::shared_ptr<std::vector<T>> data;
void check(size_type i, const std::string &msg) const;
};
template <typename T>
Blob<T>::Blob():data(std::make_shared<std::vector<T>>())
{
//构造函数中分配一个空vector，并将vector的指针保存在data中
}
// use: Blob<string> words = { "a", "an", "the"};
template <typename T>
Blob<T>::Blob(std::initializer_list<T> il):data(std::make_shared<std::vector<T>>(il))
{
}
template <typename T>
void Blob<T>::pop_back()
{
check(0, "pop_back on empty Blob");
data->pop_back();
}
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 the range");
return (*data)[i];
}
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>
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];
}
// 前置运算符
// 编译器自动会处理实参类型，不需要显式说明BlobPtr<T>&
BlobPtr& operator++()
{
check(curr, "dereference past end");
++curr;
return *this;
}
BlobPtr& operator--();
BlobPtr operator++(int);
private:
//返回一个指向vector的shared_ptr
std::shared_ptr<std::vector<T>> check(std::size_t, const std::string&) const;
// 保存一个weak_ptr,标识底层vector可能被销毁
std::weak_ptr<std::vector<T>> wptr;
std::size_t curr; // 数组总当前的位置
};
// 后置：递增对象但返回原值，此处返回值不是引用
// 在类的作用域外，就需要完整的参数声明
template <typename T>
BlobPtr<T> BlobPtr<T>::operator++(int)
{
//此时又再类的作用域内
BlobPtr ret = *this; // save curr value
++*this; // 推进一个元素;前置++检查递增是否合法
return ret;
}
#endif // BLOB_H_INCLUDED