transparent.c

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

struct helium_connection_s {
	int retain_count; 
	int foo;
};

typedef struct helium_connection_s *helium_connection_t;

struct helium_device_s {
	int retain_count;
	float blah;
};

typedef struct helium_device_s *helium_device_t;

union helium_object_u {
	helium_connection_t as_connection;
	helium_device_t as_device;
} __attribute__((transparent_union));

typedef union helium_object_u helium_object_t;

void helium_retain(helium_object_t obj) 
{
	int *retain_count_pointer = (int*)obj.as_connection;
	(*retain_count_pointer)++;
}

void helium_release(helium_object_t obj) 
{
	int *retain_count_pointer = (int*)obj.as_connection;
	(*retain_count_pointer)--;
}

int main (int argc, char const *argv[])
{
	helium_connection_t conn = calloc(sizeof(struct helium_connection_s), 1);
	helium_device_t dev = calloc(sizeof(struct helium_device_s), 1);
	
	// look ma, no casts
	printf("rcounts: %d, %d\n", conn->retain_count, dev->retain_count);
	helium_retain(conn);
	helium_retain(dev);
	printf("rcounts: %d, %d\n", conn->retain_count, dev->retain_count);
	
	return 0;
}