Partially specialize methods of variadic template classes

Question

I want to write an unmarshaller to extract arguments stored in a msgpack array for individual arguments to a call of sigc::signal::emit(...). I tried this:

Answer 1

I have always felt that the most maintainable way to specialise a member function is to defer to a specialised function object:

#include 

struct object_array
{
};


template
struct implement_do_emit
{
    template
    void operator ()(This *that, const object_array& arg) const;
};


template
struct MsgpackAdapter
{
    friend class implement_do_emit;

    virtual void do_emit(const object_array& mp_args)
    {
        auto impl = implement_do_emit();
        impl(this, mp_args);
    }

};

template
struct implement_do_emit
{
    template
    void operator ()(This *that, const object_array& arg) const
    {
        std::cout << "one type version\n";
    }
};

template
struct implement_do_emit
{
    template
    void operator ()(This *that, const object_array& arg) const
    {
        std::cout << "two type version\n";
    }
};


int main()
{
    MsgpackAdapter pi {};
    pi.do_emit(object_array());

    MsgpackAdapter pii {};
    pii.do_emit(object_array());
}