类模板+函数模板

Question

当我尝试创建一个模板类时，如下所示：

template <typename TList>
class Variant
{
public :
    std::string toString(); // var.toString()

    template<typename T>
    std::string toString(); // var.toStrint<int>();

    protected:
    template <typename T>
    std::string toString(T v); // internal Specialization

    template <>
    std::string toString(int v); // internal Specialization

    template <typename T>
    const T & get() 
    {
        std::size_t  type_index = TypeListNamespace::IndexOf<TList, T>::value ;

        if ( type_index == max_num_of_t  || type_index != _type_index)
            throw std::bad_cast() ;  

        void * ptr = (void*) &_variant_holder;
        T * vptr = reinterpret_cast<T *>(ptr);
        return *vptr; 
    }
};

// CPP FILE:

template <typename TList>
std::string Variant<TList>::toString ()
{
    // var.toString()
}

template<typename TList>
template<typename T>
std::string Variant<TList>::toString ()
{               
    return toString( get<T>() );  
}

template<typename TList>
template<typename T>
std::string Variant<TList>::toString (T v)
{                
    // no default toString method.
    return "";
}

template<typename TList>
template<>       
std::string Variant<TList>::toString (int v)
{                
    // Specialized toString for int values:
    return Core::Utility::formatString("%i", v );
}

.. other specializations ..

我得到了以下错误：

error C2244: 'Core::Variant<TList>::toString': unable to match function definition to an existing declaration
2>          Definition
2>          'std::string Core::Variant<TList>::toString(int)'
2>          Available Deklarations
2>          'std::string Core::Variant<TList>::toString(T)'
2>          'std::string Core::Variant<TList>::toString(void)'
2>          'std::string Core::Variant<TList>::toString(void)'

当我在类定义中实现这些专门化时，所有这些都是立即编译的。所以我猜我把模板语法弄错了。但是很难找到混合了类和函数模板并带有特殊化的示例。所以我最终来到了这里，希望有人能给我一个好的提示。

Answer 1

看起来你不需要把“模板<>”放在你的专业之上。

如果我删除它们，一切都编译得很好(查找不要在家中尝试这个)

template <typename TList>
class Variant
{
public :
    std::string toString(); // var.toString()

    template<typename T>
    std::string toString(); // var.toStrint<int>();

    protected:
    template <typename T>
    std::string toString(T v); // internal Specialization

    // DON'T TRY THIS AT HOME: template <>
    std::string toString(int v); // internal Specialization

    template <typename T>
    const T & get() 
    {
        std::size_t  type_index = TypeListNamespace::IndexOf<TList, T>::value ;

        if ( type_index == max_num_of_t  || type_index != _type_index)
            throw std::bad_cast() ;  

        void * ptr = (void*) &_variant_holder;
        T * vptr = reinterpret_cast<T *>(ptr);
        return *vptr; 
    }
};

// CPP FILE:

template <typename TList>
std::string Variant<TList>::toString ()
{
    // var.toString()
}

template<typename TList>
template<typename T>
std::string Variant<TList>::toString ()
{               
    return toString( get<T>() );  
}

template<typename TList>
template<typename T>
std::string Variant<TList>::toString (T v)
{                
    // no default toString method.
    return "";
}

template<typename TList>
// DON'T TRY THIS AT HOME: template<>       
std::string Variant<TList>::toString (int v)
{                
    // Specialized toString for int values:
    return Core::Utility::formatString("%i", v );
}

.. other specializations ..

Answer 2

正如您所说，您不需要template<>，因为您没有专门化该函数。

你所做的是函数重载！