just because...

gistfile1.txt

#import <objc/message.h>

typedef struct class_t {
    struct class_t *isa;
    struct class_t *superclass;
    void *cache;
    IMP *vtable;
    uintptr_t data_NEVER_USE;
} class_t;

typedef struct class_ro_t {
    uint32_t flags;
    uint32_t instanceStart;
    uint32_t instanceSize;
    const uint8_t * ivarLayout;
    const char * name;
    const void * baseMethods;
    const void * baseProtocols;
    const void * ivars;
    const uint8_t * weakIvarLayout;
    const void *baseProperties;
} class_ro_t;

typedef struct {
    SEL name;
    void *unused;
    IMP imp;
} cache_entry;


struct objc_cache {
    uintptr_t mask;
    uintptr_t occupied;
    cache_entry *buckets[1];
};

extern class_t OBJC_METACLASS_$_NSObject;
extern class_t OBJC_CLASS_$_NSObject;
static struct objc_cache objc_empty_cache_s = {
    0,
    0,
    { NULL }
};

static IMP objc_empty_vtable_s[] = {
    (IMP)&objc_msgSend
};

class_ro_t OBJC_METACLASS_RO_$_Foo = {
  1, sizeof(class_t), sizeof(class_t),
	0,
	"Foo",
	0,
	0,
	0,
	0,
	0,
};

class_ro_t OBJC_CLASS_RO_$_Foo = {
	1, sizeof(class_t), sizeof(class_t),
	0,
	"Foo",
	0,
	0,
	0,
	0,
	0,
};

class_t OBJC_METACLASS_$_Foo = {
    &OBJC_METACLASS_$_NSObject,
    &OBJC_METACLASS_$_NSObject,
    &objc_empty_cache_s,
    &objc_empty_vtable_s,
    &OBJC_METACLASS_RO_$_Foo,
};

class_t OBJC_CLASS_$_Foo = {
    &OBJC_METACLASS_$_Foo,
    &OBJC_CLASS_$_NSObject,
    &objc_empty_cache_s,
    &objc_empty_vtable_s,
    &OBJC_CLASS_RO_$_Foo
};