将 typedef-ed class 加为好友 (c++)

Question

我正在经历一些危机，我需要将类型定义的模板 class 加为好友，但我收到大量错误（太多无法粘贴到此处）。我已经放了 MRE here 这样你们就不必设置文件了。

为了完整起见，以下是 .h 文件：

//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;
}

事实上，上面的代码可以正常编译和运行。但我想将键盘和鼠标中的 SomeServerFunc 功能设为私有 class，并使 MessageHandler 成为 Keyboard 和 Mouse 的朋友。我尝试了不同的方法，但到目前为止没有任何效果。

我正在做 friend class wm::MessageHandler; 但我得到详细类型指的是 typedef 错误。然后我发现在 C++ 11 之后，您可以执行 friend wm::MessageHandler;，这会产生大量错误。我也试过了

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>;

运气不好。

非常感谢任何帮助。

Answer 1

_MessageHandler 不是 class 而是模板。试试看：

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

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

Answer 2

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

我将class声明添加到mouse.h和keyboard.h，使编译器happy.Here是代码：

#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();
        };
    }
}

将 typedef-ed class 加为好友 (c++)

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