class Foo {
    void some_method(int arg) {
        do_something;
    }
};

##</code><code>##

void some_method(SV* self, int arg) {
    // can I store the pointer as IV?
    SV* inner = SvRV(self);
    Foo* obj = (Foo*) SvIV(inner);
    obj->some_method(arg);
}