Friending a typedef-ed class (c )-CodePudding

I am going through a bit of a crisis where I need to friend a template class that is typedefed, but I am getting loads of errors(too many to paste here). I have put the MRE here so you guys don't have to set up the files.

Here are the .h files for completeness-sake:

//Keyboard.h
#pragma once
namespace wm
{
    namespace io
    {
        class Keyboard
        {
            //friend wm::MessageHandler;
        private:
            Keyboard(const Keyboard&) = delete;
            void operator=(const Keyboard&) = delete; 
            Keyboard() = default;

        public:
            static Keyboard& Instance();
            static void SomeServerFunc();

        public:
            static void SomeClientFunc();
        };
    }
}

//Mouse.h
#pragma once
namespace wm
{
    namespace io
    {
        class Mouse
        {
            //friend wm::MessageHandler;
            //friend class wm::MessageHandler; ??
        private:
            Mouse(const Mouse&) = delete;
            void operator=(const Mouse&) = delete;
            Mouse() = default;

        public:
            static Mouse& Instance();
            static void SomeServerFunc();

        public:
            static void SomeClientFunc();
        };
    }
}

//MessageHandler.h

#pragma once
#include "Keyboard.h"
#include "Mouse.h"
namespace wm
{
    template < class Keyboard, class Mouse >
    class _MessageHandler
    {
    public:
        static _MessageHandler& Instance();
        _MessageHandler(const _MessageHandler&) = delete;
        void operator=(const _MessageHandler&) = delete;

    private:
        _MessageHandler() = default;
        static void SomeMsgHandelingFunc(); //calls SomeServerFunc from window and mouse
    };

    typedef _MessageHandler<io::Keyboard, io::Mouse> MessageHandler;
}

As it is, above code compiles and runs fine. But I want to make the SomeServerFunc function in both keyboard and mouse classes private and make MessageHandler a friend of Keyboard and Mouse. I have tried different things but nothing has worked so far.

I was doing friend class wm::MessageHandler; but I got elaborated type refers to typedef error. Then I found out after c 11, you can do friend wm::MessageHandler; which gives loads of error. I also tried

friend wm::_MessageHandler<io::Keyboard, io::Mouse>;

friend class wm::_MessageHandler<io::Keyboard, io::Mouse>;

friend wm::_MessageHandler<Keyboard, Mouse>;

friend class wm::_MessageHandler<Keyboard, Mouse>;

No luck.

Would really appreciate any help.

CodePudding user response：

The _MessageHandler is not a class but a template. Try that:

namespace wm
{
    template<class Keyboard, class Mouse> class MessageHandler;

    namespace io
    {
        class Keyboard
        {
            template<class Keyboard, class Mouse> friend class wm::MessageHandler;
            ...
        };
    }
}

CodePudding user response：

to make the SomeServerFunc function in both keyboard and mouse classes private and make MessageHandler a friend of Keyboard and Mouse.

I add class declaration to mouse.h and keyboard.h,to make the compiler happy.Here is the code:

#pragma once

namespace wm
{
    template < class Keyboard, class Mouse >
    class _MessageHandler;
    namespace io
    {
        class Keyboard;
        class Mouse
        {
        friend class _MessageHandler<io::Keyboard, io::Mouse>;
        private:
            Mouse(const Mouse&) = delete;
            void operator=(const Mouse&) = delete;
            Mouse() = default;

        public:
            static Mouse& Instance();
        private:
            static void SomeServerFunc();

        public:
            static void SomeClientFunc();
        };
    }
}

#pragma once

namespace wm
{
    template < class Keyboard, class Mouse >
    class _MessageHandler;
    namespace io
    {
        class Mouse;
        class Keyboard
        {
        friend class _MessageHandler<io::Keyboard, io::Mouse>;
        private:
            Keyboard(const Keyboard&) = delete;
            void operator=(const Keyboard&) = delete; 
            Keyboard() = default;

        public:
            static Keyboard& Instance();
        private:
            static void SomeServerFunc();

        public:
            static void SomeClientFunc();
        };
    }
}