Question

Following is an interface:

class SIM{
private:
//private data

public:
Send();
Display();
Recieve();
Encrypt();
};

How do I restrict access to Display() function (it has to be lie in public part) of SIM to other classes except one class (Neo etc). I don’t want to use friend etc.

Edit:

I can move the display() to private , how do i allow only NEO class to access it? 0_o

Answer 1

You can have Display take a dummy const reference to a type that can only be created from a privately nested within the class you want to be able to make the calls. Then in order to pass that type to Display you have to be a member of that class.

But why would you do that when friend does exactly what you want?

Code example:

class AllowedCaller
{
private:
    class FriendHackHelp
    {
    };

public:
    class FriendHack
    {
    public:
        // You can only create a FriendHack from inside this class now...
        FriendHack(const FriendHackHelp&) { }
    };

    void run();
};

class Displayer
{
public:
    void Display(const AllowedCaller::FriendHack&) { /* Whatever */ }
};

void AllowedCaller::run()
{
    Displayer d;
    d.Display(FriendHack(FriendHackHelp()));
}

int main()
{
    return 0;
}