demo for traits implementation

type_traits_demo.cpp

struct built_in_type_tag{};
struct integer_type_tag : public built_in_type_tag {};
struct user_defined_type_tag{};

template<typename TypeT>
struct type_traits
{
    typedef typename TypeT::type_category type_category;
};

template<>
struct type_traits<int>
{
    typedef integer_type_tag type_category;
};

class BLA
{
    public:
        class type_info
        {
            public:
                typedef user_defined_type_tag type_category;
        };
};

template<typename T>
string doTypeCheck(const T& obj, built_in_type_tag)
{
    return "built-in type detected\n";
}

template<typename T>
string doTypeCheck(const T& obj, user_defined_type_tag)
{
    return "user-defined type detected\n";
}

template<typename T>
string TypeCheck(const T& obj)
{
    return doTypeCheck(obj, typename type_traits<T>::type_category());
}

int main()
{
    int i;
    BLA::type_info bla_into;
    cout<<TypeCheck(i);
    cout<<TypeCheck(bla_into);
    return 0;
}