Question

我希望派生类是模板类的后代。那个班级取决于后代的成员。简而言之，我想要编译这段代码：

struct IBootParams
{
    virtual bool GetImmediate() = 0;
};

template <class T>
struct TBootBootParams
{
    typename T::TransType transferType;

    typename T::UseAbort_ useAbort;

    bool GetImmediate()
    {
        if ( transferType == T::e1 )
        {
            return useAbort.someFlag;
        }

        return false;
    }

};

struct BootBootParams : public TBootBootParams<BootBootParams> 
{
    enum SomeEnum
    {
        e1=0,
        e2,
        e3
    };

    struct UseAbort
    {
        bool        someFlag;           

        char        someMember;             
        int         otherMember;        
    } useAbort;

    typedef SomeEnum TransType;
    typedef UseAbort UseAbort_;
};

struct BootAltBootParams : public TBootBootParams<BootAltBootParams> 
{
    enum SomeEnum
    {
        e1=5,
        e2,
        e3
    };

    struct UseAbort
    {
        bool        someFlag;           

        long long       someMember;             
        long long       otherMember;        
    } useAbort;

    typedef SomeEnum TransType;
    typedef UseAbort UseAbort_;
};

int _tmain(int argc, _TCHAR* argv[])
{
    BootBootParams bp;
    BootAltBootParams bpa;

    bool f = bp.GetImmediate();
    f = bpa.GetImmediate();
}

Answer 1

你不能这样做。当编译器实例化TBootBootParams<BootBootParams>时，它尚未完全读取BootBootParams的整个定义，因此您无法从TBootBootParams的定义中访问其成员（TBootBootParams的成员函数是一个例外，因为它们稍后会被实例化）。 / p>

通常的解决方案是拥有一个特质类：

template<class T> struct TBootBootParams_traits;

template <class T>
struct TBootBootParams
{
    typename TBootBootParams_traits<T>::TransType transferType;

    typename TBootBootParams_traits<T>::UseAbort_ useAbort;

    bool GetImmediate()
    {
        if ( transferType == TBootBootParams_traits<T>::e1 )
        {
            return useAbort.someFlag;
        }

        return false;
    }

};

struct BootBootParams;
template<> struct TBootBootParams_traits<BootBootParams>
{
    enum SomeEnum
    {
        e1=5,
        e2,
        e3
    };

    struct UseAbort
    {
        bool        someFlag;           

        long long       someMember;             
        long long       otherMember;        
    };

    typedef SomeEnum TransType;
    typedef UseAbort UseAbort_;
};

struct BootBootParams : 
    public TBootBootParams<BootBootParams>, 
    public TBootBootParams_traits<BootBootParams>
{
    UseAbort_ useAbort;
};

Answer 2

没有办法可以解决这个问题。所以这是我尝试的一点点黑客：

struct IBootParams
{
    virtual bool GetImmediate() = 0;
};

template <class T>
struct TBootBootParams : public IBootParams
{
    typename T::TransType transferType;

    typename T::UseAbort_ useAbort;

    virtual bool GetImmediate()
    {
        if ( transferType == T::e1 )
        {
            return useAbort.someFlag;
        }

        return false;
    }

};

struct BootBootParams_types
{
    enum SomeEnum
    {
        e1=0,
        e2,
        e3
    };

    struct UseAbort
    {
        bool        someFlag;

        char        someMember;
        int         otherMember;
    } useAbort;

    typedef SomeEnum TransType;
    typedef UseAbort UseAbort_;
};

struct BootBootParams : public BootBootParams_types,
                        public TBootBootParams<BootBootParams_types>
{
};

struct BootAltBootParams_types
{
    enum SomeEnum
    {
        e1=5,
        e2,
        e3
    };

    struct UseAbort
    {
        bool        someFlag;

        long long       someMember;
        long long       otherMember;
    } useAbort;

    typedef SomeEnum TransType;
    typedef UseAbort UseAbort_;
};

struct BootAltBootParams : public BootAltBootParams_types,
                           public TBootBootParams<BootAltBootParams_types>
{
};

int main(int argc, const char * argv[])
{
    BootBootParams bp;
    BootAltBootParams bpa;

    bool f = bp.GetImmediate();
    f = bpa.GetImmediate();
}

Answer 3

这样做你想要的吗？ It compiles.

struct IBootParams
{
    virtual bool GetImmediate() = 0;
};

template <class T>
struct TBootBootParams
{
    bool GetImmediate()
    {
        if ( static_cast<T*>(this)->transferType == T::e1 )
        {
            return static_cast<T*>(this)->useAbort.someFlag;
        }

        return false;
    }

};

struct BootBootParams : public TBootBootParams<BootBootParams> 
{
    enum SomeEnum
    {
        e1=0,
        e2,
        e3
    } transferType;

    struct UseAbort
    {
        bool        someFlag;           

        char        someMember;             
        int         otherMember;        
    } useAbort;
};

struct BootAltBootParams : public TBootBootParams<BootAltBootParams> 
{
    enum SomeEnum
    {
        e1=5,
        e2,
        e3
    } transferType;

    struct UseAbort
    {
        bool        someFlag;           

        long long       someMember;             
        long long       otherMember;        
    } useAbort;
};

int main(void)
{
    BootBootParams bp;
    BootAltBootParams bpa;

    bool f = bp.GetImmediate();
    f = bpa.GetImmediate();
}

Answer 4

我尝试对ybungalobill的解决方案进行一些改动，以计算我自己的需求。这就是我得到的

template<class T> 
struct TBootBootParams_traits;

template <class T>
struct TBootBootParams
{
    typedef TBootBootParams_traits<T> Traits;

    typename Traits::TransType transferType;
    typename Traits::UseAbort_ useAbort;

    bool GetImmediate()
    {
        if ( transferType == TBootBootParams_traits<T>::e1 )
        {
            return useAbort.someFlag;
        }

        return false;
    }
};

struct BootBootParams;
struct BootAltBootParams;

template<> 
struct TBootBootParams_traits<BootBootParams>
{
    enum SomeEnum
    {
        e1=5,
        e2,
        e3
    };

    struct UseAbort
    {
        bool        someFlag;           

        long long       someMember;             
        long long       otherMember;        
    };

    typedef SomeEnum TransType;
    typedef UseAbort UseAbort_;
};

template<> 
struct TBootBootParams_traits<BootAltBootParams>
{
    enum SomeEnum
    {
        e1=5,
        e2,
        e3
    };

    struct UseAbort
    {
        bool        someFlag;           

        int someMember;             
        float otherMember;        
    };

    typedef SomeEnum TransType;
    typedef UseAbort UseAbort_;
};

struct BootBootParams : 
    public TBootBootParams<BootBootParams>
{

};

struct BootAltBootParams : 
    public TBootBootParams<BootAltBootParams>
{

};

int main(void)
{
    BootBootParams bp;
    BootAltBootParams bpa;

    bool f = bp.GetImmediate();
    f = bpa.GetImmediate();
}

总结..我使用模板类作为此类的另一个类的必备选项，将所有类型数据放在那里。这正是我所需要的。再次感谢您的选择！

Answer 5

要使这种方法起作用，您必须将模板类对象包含为父类的成员。

在base中使用派生类'typedef

5 个答案: