msgpack base class support

base_class.cpp

#include <msgpack.hpp>
#include <sstream>
#include <cassert>
#include <iostream>

struct A {
    int a;
    MSGPACK_DEFINE(a);
};

struct B : A {
    int b;
    MSGPACK_DEFINE(MSGPACK_BASE(A), b);
};


struct C : B {
    int c;
    MSGPACK_DEFINE(MSGPACK_BASE(B), c);
};


namespace msgpack {
    inline msgpack::object base_of(msgpack::object const& o) {
        return o.via.array.ptr[0];
    }
}

int main() {
    C c;
    c.a = 1;
    c.b = 2;
    c.c = 3;

    std::stringstream ss;
    msgpack::pack(ss, c);

    auto upd = msgpack::unpack(ss.str().data(), ss.str().size());
    auto obj = upd.get();

    A a2 = obj.via.array.ptr[0].via.array.ptr[0].as<A>();
    B b2 = obj.via.array.ptr[0].as<B>();
    C c2 = obj.as<C>();

    std::cout << obj << std::endl;

    assert(c.a == a2.a);

    assert(c.a == b2.a);
    assert(c.b == b2.b);

    assert(c.a == c2.a);
    assert(c.b == c2.b);
    assert(c.c == c2.c);

    A a3 = msgpack::base_of(msgpack::base_of(obj)).as<A>();
    B b3 = msgpack::base_of(obj).as<B>();

    assert(c.a == a3.a);

    assert(c.a == b3.a);
    assert(c.b == b3.b);

}