Class Template + Function Template - inline

Question

when I tried to create a template class as follows:
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 ..
I got the following error:
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)'
When I had these specializations inside the class definition all compiled right away. So I guess I made something wrong with the template syntax. But its hard to find examples with a mix of class and function templates with specialization. So I ended up here hoping for someone who has a good hint for me.

Answer 1

It seems that you dont have to put "template <>" above your specializations.
If I remove them, everything compiles fine ( look for DON'T TRY THIS AT HOME )
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

As you said, you don't need the template<>, because you didn't specialize the function.
What you did is function overloading!