C Dynamic Dispatch

dyn_dispatch.c

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

#define container_of(ptr, type, member) ({                      \
        const typeof( ((type *)0)->member ) *__mptr = (ptr);    \
        (type *)( (char *)__mptr - offsetof(type,member) );})

struct Petable
{
	void (*pet)(struct Petable *this);
};

struct Cat
{
	struct Petable petable;
   const char *name;
};

static void _cat_pet(struct Petable *petable_this)
{
	struct Cat *this = container_of(petable_this, struct Cat, petable);
	printf("%s the cat was pet.  Meow!\n", this->name);
}

struct Cat* cat_init(const char *name)
{
	struct Cat *cat = malloc(sizeof(struct Cat));

	if( cat ) {
		cat->petable.pet = _cat_pet;
		cat->name = name;
		return cat;
	}
	else {
		return NULL;
	}
}

void cat_destroy(struct Cat *cat)
{
	if( cat ) {
		free(cat);
	}
}

struct Dog
{
	const char *masters_name;
	struct Petable petable;
};

static void _dog_pet(struct Petable *petable_this)
{
	struct Dog *this = container_of(petable_this, struct Dog, petable);
	printf("%s's dog was pet.  Woof!\n", this->masters_name);
}

struct Dog* dog_init(const char *masters_name)
{
	struct Dog *dog = malloc(sizeof(struct Dog));

	if( dog ) {
		dog->masters_name = masters_name;
		dog->petable.pet = _dog_pet;
		return dog;
	}
	else {
		return NULL;
	}
}

void dog_destroy(struct Dog *dog)
{
	if( dog ) {
		free( dog );
	}
}

void love_on_petable_animal(struct Petable *petable)
{
	petable->pet(petable);
}

int main()
{
	struct Cat *cat = cat_init("Sparkles");
	struct Dog *dog = dog_init("moncasa");

	if( !cat || !dog ) {
		goto error_cleaup;
	}

	love_on_petable_animal(&cat->petable);
	love_on_petable_animal(&dog->petable);

error_cleaup:
	cat_destroy(cat);
	dog_destroy(dog);

	return 0;
}