Is C ++ Peer Friendship Healthy?

Question

Although class friendship is one of the latest C ++ resorts, does this template make sense?

class Peer
{
public:
    friend class Peer;
    void GetSecret(const Peer& other)
    {
        const std::string& secret = other.GiveSecret();
        std::cout << secret << std::endl;
    }

private:
    const std::string& GiveSecret() const
    {
        return "secrety stuff";
    }
};

int main(int argc, char* argv[])
{
    Peer peerA;
    Peer peerB;
    peerA.GetSecret(peerB);
    return 0;
}

Well, the reason for this pattern is that Peers have the same rank and they need to share knowledge with each other, but this knowledge is secret, because no one except peers should use it, or the program is no longer valid.

One very real example: when one peer instance is created from another peer, it needs to access secret information from its original partner, but again there is no reason for anyone else to know about these internal components, just peers.

Answer 1

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Answer 2

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Answer 3

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Answer 4

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// This class defines an interface that allows selected classes to
// manipulate otherwise private data.
class SharedData
{
public:
    // Set some shared data.
    virtual void SettorA(int value) = 0;

    // Get some shared data.
    virtual bool GettorB(void) const;
};


// This class does something with the otherwise private data.
class Worker
{
public:
    void DoSomething(SharedData & data)
    {
        if (data.GettorB() == true)
        {
            data.SettorA(m_id);
        }
    }

private:
    int m_id;
};

// This class provides access to its otherwise private data to
// specifically selected classes.  In this example the classes
// are selected through a call to the Dispatch method, but there
// are other ways this selection can be made without using the
// friend keyword.
class Dispatcher
    : private SharedData
{
public:
    // Get the worker to do something with the otherwise private data.
    void Dispatch(Worker & worker)
    {
        worker.DoSomething(*this);
    }

private:
    // Set some shared data.
    virtual void SettorA(int value)
    {
        m_A = value;
    }

    // Get some shared data.
    virtual bool GettorB(void) const
    {
        return (m_B);
    }

    int    m_A;
    bool   m_B;
};

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Answer 5

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Answer 6

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Answer 7

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Answer 8

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class Sub
    : public Base
{
public:
    Sub(const std::string & name)
        : Base(),
          m_name(name)
    {
    }

    Sub(const Sub & src)
        : Base(src),
          m_id(src.m_name)
    {
    }

    Sub & operator=(const Sub & rhs)
    {
        if (&rhs != this)
        {
            Base::operator=(rhs);

            m_name = rhs.m_name;
        }

        return (this);
    }

protected:
    virtual Debug(void)
    {
        std::cout << "Sub [m_name = " << m_name << "]" << std::endl
                  << "+- ";

        Base::Debug();
    }

private:
    std::string m_name;
};

class Base
{
public:
    Base(int id)
        : m_id(id)
    {
    }

    Base(const Base & src)
        : m_id(src.m_id)
    {
    }

    Base & operator=(const Base & rhs)
    {
        if (&rhs != this)
        {
            m_id = rhs.m_id;
        }

        return (this);
    }

protected:
    virtual Debug(void)
    {
        std::cout << "Base [m_id = " << m_id << "]" << std::endl;
    }

private:
    int m_id;
};

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