Packing a polymorphous class structure with msgpack

Question

I want to pack my C++ class structure with msgpack using some polymorphous mechanism to apply code packing base classes only once.

Currently, I am packing the data twice, in the base class and in the subclass.

This is my current status:

class Base {

    public:
        template <typename Packer>
        void msgpack_pack(Packer& pk) const
        {
            pk.pack_map(1);

            pk.pack("key");
            pk.pack("value");
        }
};

class Subclass : public Base {

    public:
        template <typename Packer>
        void msgpack_pack(Packer& pk) const
        {
            pk.pack_map(2);

            // code repetition
            pk.pack("key");
            pk.pack("value");
            //////////////////

            pk.pack("child_key");
            pk.pack("child_value");
        }
};

I want to get rid of the lines in between "code repetition" but I am currently now aware of how to achieve this. Would be nice if someone had an idea.

score 2 · Accepted Answer · answered Jan 14 '19 at 14:48

You might factorize and call base class. but it need some split before:

class Base
{
protected:
    template <typename Packer>
    void msgpack_pack_content(Packer& pk) const
    {
        pk.pack("key");
        pk.pack("value");
    }
public:
    template <typename Packer>
    void msgpack_pack(Packer& pk) const
    {
        pk.pack_map(1);
        msgpack_pack_content(pk);
    }
};

class Subclass : public Base {
    template <typename Packer>
    void msgpack_pack_content(Packer& pk) const
    {
        Base::msgpack_pack_content(pk);
        //////////////////

        pk.pack("child_key");
        pk.pack("child_value");
    }
public:
    template <typename Packer>
    void msgpack_pack(Packer& pk) const
    {
        pk.pack_map(2);

        msgpack_pack_content(pk);
    }
};

Thank you. This is almost the solution I tried before but without templating "msgpack_pack_content" so msgpack could not recognize some custom members of "Subclass". But this way it works. — Robert_Jordan, Jan 15 '19 at 09:42

Packing a polymorphous class structure with msgpack

1 Answers1