Chris M Thomasson

/* Interfaces
____________________________________________________________________*/
#include <stddef.h>


struct object_prv_vtable {
  int (*fp_destroy) (void* const);
};


struct device_prv_vtable {
  int (*fp_read) (void* const, void*, size_t);
  int (*fp_write) (void* const, void const*, size_t);
};


struct device_vtable {
  struct object_prv_vtable const object;
  struct device_prv_vtable const device;
};


struct device {
  struct device_vtable const* vtable;
};


#define object_destroy(mp_self) ( \
  (mp_self)->vtable->object.fp_destroy((mp_self)) \
)


#define device_read(mp_self, mp_buf, mp_size) ( \
  (mp_self)->vtable->device.fp_read((mp_self), (mp_buf), (mp_size)) \
)


#define device_write(mp_self, mp_buf, mp_size) ( \
  (mp_self)->vtable->device.fp_write((mp_self), (mp_buf), (mp_size)) \
)






/* Sample Header (usb_drive.h)
____________________________________________________________________*/
#if ! defined(USB_HEADER_H)
#define USB_HEADER_H


extern int usb_drive_create(struct device** const);


#endif







/* Sample Impl (usb_drive.c)
____________________________________________________________________*/
/* #include "usb_drive.c" */
#include <stdio.h>
#include <stdlib.h>


struct usb_drive {
  struct device device;
  /* whatever */
};


static int usb_drive_object_destroy(void* const);
static int usb_drive_device_read(void* const, void*, size_t);
static int usb_drive_device_write(void* const, void const*, size_t);


static struct device_vtable const g_table = {
  { /* object */
    usb_drive_object_destroy
  },

  { /* device */
    usb_drive_device_read,
    usb_drive_device_write
  }
};


int usb_drive_create(
 struct device** const pself
) {
  struct usb_drive* const self = malloc(sizeof(*self));
  if (self) {
    self->device.vtable = &g_table;
    *pself = &self->device;
    return 0;
  }
  return -1;
}


int usb_drive_object_destroy(
 void* const self_
) {
  struct usb_drive* const self = self_;
  printf("usb_drive_object_destroy(%p)\n", (void*)self);
  free(self_);
  return 0;
}


int usb_drive_device_read(
 void* const self_,
 void* buf,
 size_t size
) {
  struct usb_drive* const self = self_;
  printf("usb_drive_device_read(%p, %p, %lu)\n",
    (void*)self, buf, (unsigned long)size);
  return 0;
}


int usb_drive_device_write(
 void* const self_,
 void const* buf,
 size_t size
) {
  struct usb_drive* const self = self_;
  printf("usb_drive_device_write(%p, %p, %lu)\n",
    (void*)self, buf, (unsigned long)size);
  return 0;
}







/* Sample Application
____________________________________________________________________*/
void read_write(
 struct device* const self
) {
  char buf[100];

  device_read(self, buf, 50);

  device_write(self, buf, 5);
}


int main(void) {
  struct device* a_device;

  if (! usb_drive_create(&a_device)) {
    read_write(a_device);

    object_destroy(a_device);
  }

  return 0;
}