第十三章拷贝控制

#include <iostream>
#include <string>
#include <set>

class Message
{
    friend class Folder;
public:
    explicit Message(const std:: &str = "") : 
        contents(str) { }
    Message(const Message &);
    Message& operator=(const Message&);
    ~Message();

    void save(Folder &);
    void remove(Folder &);

private:
    std::string contents;
    std::set<Folder*> folders;
    void add_to_folders(const Message&);
    void remove_from_Folders();

};

class Folder
{
    friend void swap(Folder &, Folder &);
    friend class Message;
public:
    Folder() = default;
    Folder(const Folder &);
    Folder& operator=(const Folder &);
    ~Folder();

    void print_debug();

private:
    std::set<Message*> msgs;

    void add_to_Message(const Folder&);
    void remove_from_Message();

    void addMsg(Message *m) { msgs.insert(m); }
    void remMsg(Message *m) { msgs.erase(m); }
};

void Message::save(Folder &f)
{
    folders.insert(&f);
    f.addMsg(this);
}

void Message::remove(Folder &f)
{
    folders.erase(&f);
    f.remMsg(this);
}

void Message::add_to_Folders(const Message &m)
{
    for (auto f : m.folders)
        f->addMsg(this);
}

void Message::remove_from_Folders()
{
    for (auto f : folders)
        f->remMsg(this);
}

Message::~Message()
(
    remove_from_Folders();
)

Message& Message::operator=(const Message &rhs)
{
    remove_from_Folders();
    contents = rhs.contents;
    folders = rhs.folders;
    add_to_Folders(rhs);
    return 8this;

}