Dynamic Extending vtable attempt...

#include <stdlib.h>
#include <stdio.h>
#include <string.h>


/* Object Interface
__________________________________________________*/
typedef void(*ct_iobject_fp_destroy) (void*);
typedef void(*ct_iobject_fp_print) (void*, FILE*);

struct ct_iobject_vtable
{
    ct_iobject_fp_destroy fp_destroy;
    ct_iobject_fp_print fp_print;
};

#define ct_iobject_vtable(mp_self) \
    ((((struct ct_iobject_vtable*)(*((void**)(mp_self)))))

#define ct_iobject_print(mp_self, mp_file) \
    (ct_iobject_vtable(mp_self)->fp_print((mp_self), (mp_file))))

#define ct_iobject_destroy(mp_self) \
    (ct_iobject_vtable(mp_self)->fp_destroy((mp_self))))


/* Person Interface
__________________________________________________*/
typedef void(*ct_person_fp_talk) (void*, char const*, FILE*);

struct ct_person_vtable
{
    struct ct_iobject_vtable m_object;
};

struct ct_person_prv_vtable
{
    ct_person_fp_talk fp_talk;
};

#define ct_iperson_talk(mp_self, mp_msg, mp_file) \
    ((mp_self)->m_prv_vtable.fp_talk((mp_self), (mp_msg), (mp_file)))

static void ct_person_print(void* raw_self, FILE* file);
static void ct_person_talk(void* raw_self, char const* msg, FILE* file);
static void ct_person_destroy(void* raw_self);

static struct ct_person_vtable const g_ct_person_vtable = {
    {
        ct_person_destroy,
        ct_person_print
    }
};


/* Person Impl
__________________________________________________*/
struct ct_person
{
    struct ct_person_vtable const* m_vtable;
    struct ct_person_prv_vtable m_prv_vtable;
    char* name;
};

static int
ct_person_create(
    struct ct_person* const self,
    char const* name
) {
    size_t name_size = strlen(name) + 1;

    self->name = calloc(1, name_size);

    if (self->name)
    {
        strcpy(self->name, name);

        // setup vtable
        self->m_vtable = &g_ct_person_vtable;
        self->m_prv_vtable.fp_talk = ct_person_talk;

        printf("(%p:ct_person_create):(name:%s)\n",
            (void*)self, self->name);

        return 0;
    }

    return -1;
}

static void
ct_person_print(
    void* raw_self,
    FILE* file
) {
    struct ct_person* const self = raw_self;

    fprintf(file, "(%p:ct_person_print):(name:%s)\n",
        (void*)self, self->name);
}

static void
ct_person_talk(
    void* raw_self,
    char const* msg,
    FILE* file
) {
    struct ct_person* const self = raw_self;

    fprintf(file, "(%p:ct_person_talk):(name:%s says %s)\n",
        (void*)self, self->name, msg);
}

static void
ct_person_destroy(
    void* raw_self
) {
    struct ct_person* const self = raw_self;

    printf("(%p:ct_person_destroy):(name:%s)\n",
        (void*)self, self->name);

    free(self->name);
}



/* Employee Interface
__________________________________________________*/
static void ct_employee_print(void* raw_self, FILE* file);
static void ct_employee_destroy(void* raw_self);

static struct ct_person_vtable const g_ct_employee_vtable = {
    {
        ct_employee_destroy,
        ct_employee_print
    }
};


/* Employee Impl
__________________________________________________*/
struct ct_employee
{
    struct ct_person m_person;
    int id;
};

static int
ct_employee_create(
    struct ct_employee* const self,
    char const* name,
    int id
) {
    int status = ct_person_create(&self->m_person, name);

    if (!status)
    {
        // setup vtable
        self->m_person.m_vtable = &g_ct_employee_vtable;

        self->id = id;

        return 0;
    }

    return status;
}

static void
ct_employee_print(
    void* raw_self,
    FILE* file
) {
    struct ct_employee* const self = raw_self;

    fprintf(file, "(%p:ct_employee_print):(id:%d)\n",
        (void*)self, self->id);

    // explicit chain
    ct_person_print(&self->m_person, file);
}

static void
ct_employee_destroy(
    void* raw_self
) {
    struct ct_employee* const self = raw_self;

    printf("(%p:ct_employee_destroy):(id:%d)\n",
        (void*)self, self->id);

    // explicit chain
    ct_person_destroy(&self->m_person);
}


/* Testing 123...
__________________________________________________*/
int main(void)
{
    struct ct_employee employee;

    if (!ct_employee_create(&employee, "Chris M. Thomasson", 103))
    {
        struct ct_person* const person = &employee.m_person;

        ct_iperson_talk(person, "Hello World!", stdout);
        ct_iobject_print(&employee, stdout);
        ct_iobject_destroy(person);
    }

    printf("\n_______________________________________\n");

    if (!ct_employee_create(&employee, "Jane Doe", 1203))
    {
        struct ct_person* const person = &employee.m_person;

        ct_iobject_print(person, stdout);
        ct_iperson_talk(person, "Goodbye", stdout);
        ct_iobject_destroy(&employee);
    }

    return 0;
}