13.2.1

13.23
有一定差异，我使用if判断是否自我拷贝
本节使用先拷贝右侧对象的方式来使自我拷贝正常运行

13.24
如果没有定义析构函数，肯定会发生内存泄露
如果没有定义拷贝构造函数，当使用了拷贝构造函数时，删除一个对象会使和其他对象共用的内存被释放，其他对象则出现错误

13.25
拷贝构造和拷贝赋值必须新建内存，而不是和右侧共用内存

当shared_ptr计时器为0时，会自动的释放，所以不需要析构函数

13.26
@pezy

https://github.com/PYPARA/Cpp-Primer/blob/master/ch13/ex13_26.h

#include <vector>
#include <string>
#include <initializer_list>
#include <memory>
#include <exception>

using std::vector; using std::string;

class ConstStrBlobPtr;

class StrBlob {
public:
    using size_type = vector<string>::size_type;
    friend class ConstStrBlobPtr;

    ConstStrBlobPtr begin() const;
    ConstStrBlobPtr end() const;

    StrBlob():data(std::make_shared<vector<string>>()) { }
    StrBlob(std::initializer_list<string> il):data(std::make_shared<vector<string>>(il)) { }

    // copy constructor
    StrBlob(const StrBlob& sb) : data(std::make_shared<vector<string>>(*sb.data)) { }
    // copyassignment operators
    StrBlob& operator=(const StrBlob& sb);

    size_type size() const { return data->size(); }
    bool empty() const { return data->empty(); }

    void push_back(const string &t) { data->push_back(t); }
    void pop_back() {
        check(0, "pop_back on empty StrBlob");
        data->pop_back();
    }

    std::string& front() {
        check(0, "front on empty StrBlob");
        return data->front();
    }

    std::string& back() {
        check(0, "back on empty StrBlob");
        return data->back();
    }

    const std::string& front() const {
        check(0, "front on empty StrBlob");
        return data->front();
    }
    const std::string& back() const {
        check(0, "back on empty StrBlob");
        return data->back();
    }

private:
    void check(size_type i, const string &msg) const {
        if (i >= data->size()) throw std::out_of_range(msg);
    }

private:
    std::shared_ptr<vector<string>> data;
};

class ConstStrBlobPtr {
public:
    ConstStrBlobPtr():curr(0) { }
    ConstStrBlobPtr(const StrBlob &a, size_t sz = 0):wptr(a.data), curr(sz) { } // should add const
    bool operator!=(ConstStrBlobPtr& p) { return p.curr != curr; }
    const string& deref() const { // return value should add const
        auto p = check(curr, "dereference past end");
        return (*p)[curr];
    }
    ConstStrBlobPtr& incr() {
        check(curr, "increment past end of StrBlobPtr");
        ++curr;
        return *this;
    }

private:
    std::shared_ptr<vector<string>> check(size_t i, const string &msg) const {
        auto ret = wptr.lock();
        if (!ret) throw std::runtime_error("unbound StrBlobPtr");
        if (i >= ret->size()) throw std::out_of_range(msg);
        return ret;
    }
    std::weak_ptr<vector<string>> wptr;
    size_t curr;
};

ConstStrBlobPtr StrBlob::begin() const // should add const
{
    return ConstStrBlobPtr(*this);
}
ConstStrBlobPtr StrBlob::end() const // should add const
{
    return ConstStrBlobPtr(*this, data->size());
}

StrBlob& StrBlob::operator=(const StrBlob& sb)
{
    data = std::make_shared<vector<string>>(*sb.data);
    return *this;
}

int main()
{
    return 0;
}